# 6.2. Reading the Aria log file

Every Aria run outputs a log file with details about the simulation progress. By default this file is named based on the input file name (so an input of `aria.i` would produce a log file `aria.log`). This can be overridden when launching Aria by using the `-o` option, as in `aria -i aria.i -o sierra.log`. Log files are overwritten, so a subsequent launch of the same input file will by default override any prior log files.

The following sections go through the different parts of the log file and how to interpret the information shown in each section. If a simulation encounters an error or produces unexpected behavior, the first place you should look is in the log file.

## 6.2.1. Preamble

The first thing in the log file is a preamble that shows the Sandia legal statement, when and where the job was run, and what version of Aria was used.

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----

                                          Aria

                     Coupled multiphysics including Navier-Stokes,
                    elasticity, energy transport, species transport,
                      electrostatics;  free and moving boundaries;
                               transient or steady state.

                               Version 5.10.1-0-g1b0c0bcd

                           With coupled mechanics support for
                              Aria - Coupled multiphysics
                     Encore - Solution Verification Analysis Region

                              Sandia National Laboratories
                   Albuquerque, New Mexico and Livermore, California

                         Please email questions and comments to
                                 sierra-help@sandia.gov

                     Notice: This computer software was prepared by
                     National Technology and Engineering Solutions
                         of Sandia, hereinafter the Contractor,
                         under Contract DE-NA-0003525 with the
                     Department of Energy (DOE).  All rights in the
                    computer software are reserved by DOE on behalf
                        of the United States Government and the
                    Contractor as provided in the Contract. You are
                      authorized to use this computer software for
                       Governmental purposes but it is not to be
                     released or distributed to the public. NEITHER
                      THE U.S. GOVERNMENT NOR THE CONTRACTOR MAKES
                    ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY
                        LIABILITY FOR THE USE OF THIS SOFTWARE.

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----

            Directory /scratch/aria/demo
           Executable /projects/sierra/linux_rh7/install/5.10.1/bin/aria
                Built Sep 19 2022 19:07:04
        Build Options linux intel-2021.3.0 release
          Run Started Oct  6 2022 15:52:24
                 User sierra
         Architecture ceerws123
                 Host ceerws123
             Hardware x86_64
              Running Linux
           Processors 1
    Simd vector width 2

          Product               Version         Qualifier
    -------------------- ---------------------- ----------
                    ACME 2.9.0
                    Aria 5.10.1-0-g1b0c0bcd
               Chaparral 3.3.1 development      unreleased
                  Encore 5.10.1-0-g1b0c0bcd
                   Linux 3.10.0-1127.el7.x86_64
        SIERRA Framework 5.10.1-0-g1b0c0bcd
    Sandia Toolkit (STK) 5.10.1-0-g1b0c0bcd
                Trilinos 13.5.0
              UtilityLib 5.10.1-0-g1b0c0bcd
           not specified

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----

In this example, aria `5.10.1` was used for this run, which was built on September 19, 2022. The suffix after the version number (`-0-g1b0c0bcd`) gives a SHA for which commit this version of the code was built with. The summary also shows that the job was launched on October 6, 2022 on a ceerws blade using 1 processor in the `/scratch/aria/demo` directory by the `sierra` user.

## 6.2.2. Input File

The first thing shown after the preamble is an echo of the input file. If there were any aprepro commands in the input file, those are resolved before this is printed so this is a reflection of the actual commands parsed by Aria. This section is also where any parsing errors will be shown, at the line where the error was detected. The log file echo will be immediately after this line

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----
    Reading aria.i                                              Oct  6 2022 15:52:28

## 6.2.3. Initialization

The instantiation section of the log file is shown after the following line

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----
    Instantiating system                                        Oct  6 2022 15:52:28

This section is largely diagnostic, showing defaults and sometimes warnings or errors that may encountered during problem setup. Searching this section for the keyword “warning” can sometimes be useful to ensure that nothing unexpected is being assumed.

The procedure initialization comes after the instantiation section, and has information like a list of available variables for output.

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----
    Initializing procedure                                      Oct  6 2022 15:52:28

    Aria Region "myRegion" has the following fields available for output:
      NODE_RANK Fields:
        * solution->PRESSURE
        * solution->PRESSURE_STKFS_OLD
        * solution->TEMPERATURE
        * solution->TEMPERATURE_STKFS_OLD
        * solution->VELOCITY
        * solution->VELOCITY_STKFS_OLD
      FACE_RANK Fields:
        * face_coverage
      ELEMENT_RANK Fields:
        * current_element_volume
        * initial_element_volume
        * volume_change_ratio
      Global Variables:
        * abv_5
        * CFL_MAX
        * CFL_MIN

## 6.2.4. Run-Time Reporting

After the preamble of the log file comes the actual execution of the model, including linear and nonlinear solver information, time stepping, and variable calculation. The information contained in this section can help determine whether the model is stable and if correct results are being obtained. To illustrate this section of the log file, one time step of the run is shown below and will be further explained in the following sections.

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----
    Minimum Time Step Selection:
            min           max
    Time step selection: dt  = 5.287e+00 (Chemistry minimum timestep).
         1.000e-02     5.287e+00     AriaRegion
    Transient Time_Block_2: dt = 5.287
    ---------------------------------------------------
    Transient Time_Block_2, step 169, time 2.1985e+03, time step 5.2875e+00, 61.06% complete
    ---------------------------------------------------
    Advance AriaRegion, time 2198, time step 5.287

    Memory Usage: current = 209186816 (199.5 M), high-water-mark = 217268224 (207.2 M)

    Equation System AriaRegion->main:
     * Step  : Transient, Strategy: NEWTON, Time: 2.20e+03, Step: 5.29e+00
     * Matrix: Solver: "Solve_Temperature", Unknowns: 1360, Nonzeros: 11578
     * Mesh  : Processor 0 of 1: 1253 of 1253 elems, 1363 of 1363 nodes
     * Computing View Factors for enclosure space
      N O N L I N E A R                L I N E A R
    ----------------------   ------------------------------------
    Step  Resid    Delta     Itns Status  Resid    Asm/Slv Time
    ---- -------- --------   ---- ------ -------- ---------------
    1    6.37e-02 1.10e+01   59    ok    8.23e-07 7.0e-03/2.0e-03
    2    1.10e-04 8.18e-03   58    ok    1.19e-09 7.0e-03/2.0e-03
    3    3.06e-07 8.81e-05   61    ok    3.68e-12 6.0e-03/2.0e-03
    Termination reason: 8.80515e-05 < nonlinear_correction_tolerance(0.001)

    Field            min     @ id    max     @ id max-chg  @ id pred-err  pred-min  @ id  pred-max  @ id
    ------------- ---------- ---- ---------- ---- -------- ---- -------- ---------- ---- ---------- ----
    * TEMPERATURE 3.8650e+02  412 8.4155e+02  512 3.93e+00 1443 3.53e-04 3.8650e+02  412 8.4155e+02  512

    DT_TEMPERATURE : MIN(value,loc) = (-1.18e+00, 1443) : MAX(value,loc) = (9.68e-01, 249)
    Segregated solution procedure converged after 1 iterations.
    -------------- For equation system name: main --------------
    Global predictor error = 3.531e-04
    Time step selection: dt <= 2.326e+01 (based on Predictor-Corrector Tolerance).
    Time step selection: dt <= 1.057e+01 (based on Maximum Time Step Size Ratio).
    Time step selection: dt <= 6.000e+01 (based on Maximum Time Step Size).
    Time step selection: dt  = 5.277e+00 (Minimum Chemistry timestep block_6).
    Time step selection: dt <= 1.277e+01 (based on Stability limit for dt Ratio).
    Time step selection: dt  = 1.057e+01 (Adaptive time stepping result).
    Killed  1 elements this timestep, for a total of 87 dead.
            Global Variable               Value
    -------------------------------- ----------------
    Conv_ipo                         189.224
    Conv_ipo_surface_block_2_edge2_2 0
    Conv_ipo_surface_block_3_edge2_2 0
    killed_elements                  1
    space_area                       0.155955
    Tmax                             386.498 841.553
    total_dead_elements              87
    Region::execute() time for AriaRegion: 3.537e+00 sec.

### 6.2.4.1. Current Time information

The first part of the above section deals with the time step and temporal information about the running model. This section can be seen below:

    +----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----
    Minimum Time Step Selection:
            min           max
    Time step selection: dt  = 5.287e+00 (Chemistry minimum timestep).
         1.000e-02     5.287e+00     AriaRegion
    Transient Time_Block_2: dt = 5.287
    ---------------------------------------------------
    Transient Time_Block_2, step 169, time 2.1985e+03, time step 5.2875e+00, 61.06% complete
    ---------------------------------------------------
    Advance AriaRegion, time 2198, time step 5.287

Aria determined the current time step size based on factors from the previous time step. Here, the maximum allowed time step size is 5.287, which is based on the minimum time step allowed for the chemistry model. It can also be seen that the run is currently in `Time_Block_2` as is set up in Solution Control.

The information contained within the dotted lines allows one to gauge how far along a simulation is. In that one line, one can find the current time block, the iteration number, current simulation time, current time step, and the percent completion of the current time block.

### 6.2.4.2. Linear/Nonlinear Solves

The next part of the runtime information deals with the linear and nonlinear solution:

    Equation System AriaRegion->main:
     * Step  : Transient, Strategy: NEWTON, Time: 2.20e+03, Step: 5.29e+00
     * Matrix: Solver: "Solve_Temperature", Unknowns: 1360, Nonzeros: 11578
     * Mesh  : Processor 0 of 1: 1253 of 1253 elems, 1363 of 1363 nodes
     * Computing View Factors for enclosure space
      N O N L I N E A R                L I N E A R
    ----------------------   ------------------------------------
    Step  Resid    Delta     Itns Status  Resid    Asm/Slv Time
    ---- -------- --------   ---- ------ -------- ---------------
    1    6.37e-02 1.10e+01   59    ok    8.23e-07 7.0e-03/2.0e-03
    2    1.10e-04 8.18e-03   58    ok    1.19e-09 7.0e-03/2.0e-03
    3    3.06e-07 8.81e-05   61    ok    3.68e-12 6.0e-03/2.0e-03
    Termination reason: 8.80515e-05 < nonlinear_correction_tolerance(0.001)

    Field            min     @ id    max     @ id max-chg  @ id pred-err  pred-min  @ id  pred-max  @ id
    ------------- ---------- ---- ---------- ---- -------- ---- -------- ---------- ---- ---------- ----
    * TEMPERATURE 3.8650e+02  412 8.4155e+02  512 3.93e+00 1443 3.53e-04 3.8650e+02  412 8.4155e+02  512

    DT_TEMPERATURE : MIN(value,loc) = (-1.18e+00, 1443) : MAX(value,loc) = (9.68e-01, 249)
    Segregated solution procedure converged after 1 iterations.

Each bullet point here gives some information as to the solution time and strategy, as well as some information about the matrix being solved. The line `Computing View Factors ...` indicates that enclosure radiation viewfactors are being solved.

The meanings of each column of the `NONLINEAR/LINEAR` table are shown in the list below.

Step

  The nonlinear step being taken - here there are three nonlinear steps in the timestep

Resid

  Nonlinear residual at the end of each nonlinear step and before the linear steps are taken

Delta

  Difference in the solution variable(s) compared to the last nonlinear solution

Itns

  Number of linear iterations per nonlinear step

Status

  Whether linear solver completed successfully (output is either ok or an error code or message)

Resid

  Linear residual at the end of the linear iterations

Asm/Slv Time

  Linear system assembly/solve times

This section of the log file also shows the reason why the time step exited - usually due to reaching some desired tolerance or failure to converge. Here, the solution was reached when the change in temperature from the previous nonlinear step (`Delta = 8.81e-05`) was less than the nonlinear correction tolerance of 0.001.

The lines below the table also show useful output on the fields being solved - here, for temperature. We can see that the minimum temperature is 386.5 at node 412, and the maximum temperature is 841.6 at node 512. Information about the predictor-corrector errors are also shown, as well as the time derivative of temperature.

### 6.2.4.3. Timestep Determination

Based on the solution at the current step, the timestep is re-calculated. This is shown in the following lines:

    -------------- For equation system name: main --------------
    Global predictor error = 3.531e-04
    Time step selection: dt <= 2.326e+01 (based on Predictor-Corrector Tolerance).
    Time step selection: dt <= 1.057e+01 (based on Maximum Time Step Size Ratio).
    Time step selection: dt <= 6.000e+01 (based on Maximum Time Step Size).
    Time step selection: dt  = 5.277e+00 (Minimum Chemistry timestep block_6).
    Time step selection: dt <= 1.277e+01 (based on Stability limit for dt Ratio).
    Time step selection: dt  = 1.057e+01 (Adaptive time stepping result).

These restrictions will change based on the method in which the solution is solved as well as the physics being solved. Here, the timestep may be limited by adaptive time stepping restrictions (predictor-corrector tolerance, maximum timestep ratio, and maximum time step size), chemistry timestep, and BDF2 stability limit. One can see that the Chemistry timestep of 5.28s is the limiting timestep, and this will be the timestep size which is used in the next timestep. See Time Step Selection for more information.

### 6.2.4.4. Global Variable Output

At the end of each timestep, a summary is given of the global variables in the model. If there are global variables that the user does not wish to output the `GLOBAL VARIABLES EXCLUDED FROM LOG FILE = [list of variables]` input deck line may be used.

            Global Variable               Value
    -------------------------------- ----------------
    Conv_ipo                         189.224
    Conv_ipo_surface_block_2_edge2_2 0
    Conv_ipo_surface_block_3_edge2_2 0
    killed_elements                  1
    space_area                       0.155955
    Tmax                             386.498 841.553
    total_dead_elements              87
    Region::execute() time for AriaRegion: 3.537e+00 sec.

This section is useful for run-time monitoring of key values, as well as how long the execution time was, in order to locate any slow-running parts of the model through time.

## 6.2.5. Timing Summary

Aria contains many timers which encapsulate certain operations of each simulation. The timing summary shows the results of these timers and are organized so that aspects of the model that take more time can be found. If your simulation is running slower than you expect, or you are looking for ways to speed it up, the timer section can give useful information about what parts of the simulation are most expensive.

A sample timing summary can be seen below and will be further explained:

    Timing summary of 1 processor
                     Timer                   Count       CPU Time              Wall Time
    ---------------------------------------- ----- --------------------- ---------------------
    Sierra                                       1    15:14.415 (100.0%)    15:19.072 (100.0%)
      Procedure AriaProcedure
        Initialize                               1        0.017 (<0.01%)        0.017 (<0.01%)
        Execute                                  1    15:13.010 (99.85%)    15:17.659 (99.85%)
        Mesh input                               1        0.168 ( 0.02%)        0.170 ( 0.02%)
        Mesh output                            357        0.905 ( 0.10%)        1.196 ( 0.13%)
        Region AriaRegion
          Initialize                             1        0.015 (<0.01%)        0.017 (<0.01%)
          Execute                              357    15:11.364 (99.67%)    15:15.619 (99.62%)
            Nonlinear Iteration                997       16.482 ( 1.80%)       16.568 ( 1.80%)
              Preprocessing                    997        6.811 ( 0.74%)        6.865 ( 0.75%)
                Chemistry Kinetics             997        6.768 ( 0.74%)        6.820 ( 0.74%)
              LinSys Assembly                  997        6.091 ( 0.67%)        6.119 ( 0.67%)
              LinSys Solve                     997        2.458 ( 0.27%)        2.472 ( 0.27%)
              LinSys Scatter                   997        0.276 ( 0.03%)        0.273 ( 0.03%)
              Nonlinear Utilities             3988        0.668 ( 0.07%)        0.669 ( 0.07%)
            Postprocessing                     358        0.034 (<0.01%)        0.046 (<0.01%)
            Utilities                         2144    14:51.790 (97.53%)    14:54.651 (97.34%)
              Parallel Sync                   5776        0.012 (<0.01%)        0.010 (<0.01%)
              Chaparral Viewfactor             357    14:51.546 (97.50%)    14:54.417 (97.32%)
              Chaparral Radiosity              997        0.629 ( 0.07%)        0.623 ( 0.07%)
            Chemistry Utilities               3062        0.085 (<0.01%)        0.079 (<0.01%)
            Contact Search                     357        0.003 (<0.01%)        0.000 (<0.01%)
                                              1074        0.259 ( 0.03%)        0.372 ( 0.04%)
            Tmax                               358        0.275 ( 0.03%)        0.277 ( 0.03%)
          Mesh input                             1        0.168 ( 0.02%)        0.170 ( 0.02%)
          Mesh output                          357        0.904 ( 0.10%)        1.196 ( 0.13%)
            Results output                     358        0.326 ( 0.04%)        0.420 ( 0.05%)
            Restart output                     358        0.549 ( 0.06%)        0.729 ( 0.08%)
            History output                     358        0.015 (<0.01%)        0.027 (<0.01%)
            Heartbeat output                   358        0.020 (<0.01%)        0.036 (<0.01%)
            Control                            109        0.001 (<0.01%)        0.005 (<0.01%)
            Vis output                         358        0.001 (<0.01%)        0.000 (<0.01%)
      Perf: RunSierra                            1        1.218 ( 0.13%)        1.225 ( 0.13%)
        Perf: RunSierra::parse                   1        1.218 ( 0.13%)        1.225 ( 0.13%)
        Perf: RunSierra::Domain::execute         1    15:13.197 (99.87%)    15:17.846 (99.87%)

Each entry shows the CPU and Wall Times associated with it, along with a percentage, which is the percentage of the total run time. One can also see where a timer resides with respect to the Procedure, Region, etc.~by the level of indention in the timing summary. For example, one can see by the indention that `Nonlinear Iteration` is a part of `Execute`, which resides in the `Region ariaRegion`. The sum of timers of all entries on a certain indention level should be less than or equal to the timer of the parent entry, since the parent timer is a wrapper around the children timers and the corresponding code execution.

## 6.2.6. Failed Time Step

In most cases, failure of a step leads to the timestep being reduced so that the step can be tried again. See Time Step Failure for more discussion on this. Some common ways the step can fail are included below, with examples of the corresponding log output

Nonlinear Convergence Failure

  This failure occurs when the step fails to converge in the permitted number of nonlinear iterations (see Maximum Nonlinear Iterations). If this message persists after decreasing the timestep, it can imply an ill-posed problem or material model.

      Equation System myRegion->main:
      * Step  : Transient, Strategy: NEWTON, Time: 5.75e-03, Step: 6.62e-04
      * Matrix: Solver: "solve_temperature", Unknowns: 297, Nonzeros: 4753
      * Mesh  : Processor 0 of 1: 128 of 128 elems, 297 of 297 nodes
        N O N L I N E A R                 L I N E A R
      ----------------------   --------------------------------------
      Step  Resid    Delta     Itns  Status   Resid    Asm/Slv Time
      ---- -------- --------   ---- -------- -------- ---------------
      1    1.84e+00 1.76e+01   13    ok      9.38e-11 9.7e-04/6.2e-04
      2    8.94e-01 8.28e+00   13    ok      9.14e-11 9.6e-04/6.0e-04
      3    8.53e-01 7.41e+00   14    ok      1.95e-11 9.5e-04/6.3e-04
      4    8.12e-01 7.24e+00   13    ok      2.14e-11 9.5e-04/6.1e-04
      5    6.32e-01 6.50e+00   14    ok      5.73e-11 9.5e-04/6.4e-04
      6    7.23e-01 5.63e+00   13    ok      3.23e-11 9.5e-04/5.9e-04
      7    5.11e-01 3.85e+00   14    ok      2.30e-11 9.5e-04/6.3e-04
      8    3.97e-01 1.70e+00   13    ok      5.51e-11 9.5e-04/6.0e-04
      9    3.86e-02 1.43e-01   14    ok      2.15e-11 9.5e-04/6.4e-04
      10   3.41e-04 1.63e-03   13    ok      9.07e-11 9.5e-04/6.0e-04
      reached maximum_nonlinear_iterations(10)
      Region::execute() time for myRegion: 1.78e-02 sec.
      Transient TimeBlock1 failed, step 56, time 5.0893e-03, time step 6.6206e-04

        Retrying step with a time step corresponding to time step size ratio of 0.5

Non-finite nonlinear residual norm

  This failure occurs when the linear system encounters NaN/Inf entries. If this message persists after decreasing the timestep, it can imply an ill-posed problem or material model.

      Equation System myRegion->main:
      * Step  : Transient, Strategy: NEWTON, Time: 1.00e-01, Step: 1.00e-01
      * Matrix: Solver: "solve_temperature_tpetra", Unknowns: 125, Nonzeros: 2197
      * Mesh  : Processor 0 of 2: 48 of 64 elems, 100 of 125 nodes
      Region::execute() time for myRegion: 5.82e-03 sec.
          1.000e-16     5.000e-02     myRegion
      Transient MySolveBlock failed, step 1, time 0.0000e+00, time step 1.0000e-01
      ERROR: Non-finite nonlinear residual norm.
        Retrying step with a time step corresponding to time step size ratio of 0.5

Linear Solver failure

  This failure mode happens when the linear solver fails to solve the nonlinear iteration. If these issues persist, see Linear Solver Failure for guidance on troubleshooting these errors.

      Equation System The_Region->LENS:
      * Step  : Transient, Strategy: NEWTON, Time: 5.40e-02, Step: 3.67e-04
      * Matrix: Solver: "gmres_ilut", Unknowns: 6247772, Nonzeros: 467738778
      * Mesh  : Processor 0 of 832: 13913 of 7441357 elems, 2874 of 1243618 nodes
        N O N L I N E A R                L I N E A R
      ----------------------   ------------------------------------
      Step  Resid    Delta     Itns Status  Resid    Asm/Slv Time
      ---- -------- --------   ---- ------ -------- ---------------
        1 8.02e+00 3.62e+08    165     ok 7.92e-06 9.4e-01/7.9e+00
        2 3.53e+00 4.09e+08    224     ok 3.47e-06 9.3e-01/9.9e+00
        3 3.67e+06 1.53e+15    184     ok 3.62e+00 9.3e-01/8.5e+00
      ERROR: Linear system failed due to excessive residual ratio growth.
      Region::execute() time for The_Region: 3.63e+01 sec.
      Transient The_Time_Block_1 failed, step 112, time 5.3627e-02, time step 3.6750e-04

        Retrying step with a time step corresponding to time step size ratio of 0.8

Chemistry/Radiation/Generic submodel failures

  This failure occurs when one of the submodels’ solves fails, e.g. the chemeq solver failure below

      Equation System The_Region->energy:
      * Step  : Transient, Strategy: NEWTON, Time: 1.30e+02, Step: 5.16e-02
      * Matrix: Solver: "Iterative_Solver", Unknowns: 1589, Nonzeros: 63729
      * Mesh  : Processor 0 of 4: 123 of 443 elems, 289 of 987 nodes
        N O N L I N E A R                 L I N E A R
      ----------------------   --------------------------------------
      Step  Resid    Delta     Itns  Status   Resid    Asm/Slv Time
      ---- -------- --------   ---- -------- -------- ---------------
        1 1.18e+03 9.83e+02      6       ok 1.87e-08 9.3e-03/8.0e-03
        2 1.71e+03 1.42e+03      6       ok 2.85e-08 9.7e-03/7.8e-03
        3 6.28e+02 5.11e+02      6       ok 2.36e-08 1.5e-02/7.6e-03
        4 7.14e+02 5.76e+02      6       ok 4.13e-09 1.7e-02/7.6e-03
        5 8.67e+02 6.20e+02      6       ok 1.38e-08 2.1e-02/7.7e-03
        6 1.41e+03 9.65e+02      6       ok 7.46e-08 2.5e-02/7.6e-03
        7 1.37e+03 9.42e+02      6       ok 6.65e-08 3.0e-02/7.6e-03
        8 9.76e+02 7.00e+02      6       ok 7.03e-08 3.5e-02/7.6e-03
        9 8.30e+02 6.20e+02      6       ok 6.50e-08 3.8e-02/7.6e-03
        10 2.40e+02 2.06e+02      5       ok 3.36e-08 4.1e-02/7.4e-03
        11 7.78e+02 6.09e+02      4       ok 9.48e-08 4.2e-02/6.9e-03
        12 6.53e+02 4.70e+02      4       ok 2.54e-07 4.2e-02/6.9e-03
      ChemEq ODE in material ChemeqEM model ChemeqEM on block_5:
        chemeq exited with nonzero exit status ... failed to converge.
        CVode error test failure in CVode
      Species concentrations before ODE solve:
        h2oa = 0.0622659
        h2og = 7.86947e-05
        tatb = 2.89618
        mf = 6.31361e-13
        h2om = 6.31361e-13
        gasm = 2.44478e-25
        carbonm = 1.56736e-25
        gast = 1.2128e-11
        carbont = 6.30655e-12
      Phase Pressure before ODE solve:  8070.71
      Temperature before ODE solve:  1940.37
      Rate Multiplier before ODE solve:  1
      Region::execute() time for The_Region: 4.63e-01 sec.
      Transient TimeBlock failed, step 350, time 1.30217e+02, time step 5.1644e-02
      ERROR: Chemistry failure - retrying time step
        Retrying step with a time step corresponding to time step size ratio of 0.5

Missed Phenomenon

  One may also find that a timestep is rejected because some underlying physical process was not captured, e.g.

      Equation System The_Region->energy:
      * Step  : Transient, Strategy: NEWTON, Time: 1.20e+02, Step: 1.00e+00
      * Matrix: Solver: "Iterative_Solver", Unknowns: 1589, Nonzeros: 63729
      * Mesh  : Processor 0 of 4: 123 of 443 elems, 289 of 987 nodes
        N O N L I N E A R                 L I N E A R
      ----------------------   --------------------------------------
      Step  Resid    Delta     Itns  Status   Resid    Asm/Slv Time
      ---- -------- --------   ---- -------- -------- ---------------
        1 5.16e+01 7.24e+02     14       ok 6.71e-08 1.0e-02/1.1e-02
        2 2.01e-05 2.30e+00      5       ok 2.27e-10 9.2e-03/7.4e-03
        3 8.59e-09                     NoOp          9.3e-03
      Termination reason: 8.59282e-09 < nonlinear_residual_tolerance(5e-07),
                      and 0 < nonlinear_correction_tolerance(1e-09)

      Field               min     @ id     max     @ id  max-chg  @ id  pred-err  pred-min  @ id   pred-max  @ id
      ---------------- ---------- ----- ---------- ----- -------- ----- -------- ---------- ----- ---------- -----
        DENSITY        3.5813e+01 27005 5.1571e+01 27006 1.89e+00 27005 3.10e-02 3.3922e+01 27005 5.0338e+01 27006
        SPECIES        5.1795e-01 27005 7.6904e-01 27006 3.96e-02 27006 4.49e-02 4.8946e-01 27005 7.2940e-01 27006
        SPECIES_carbon 2.9143e-13 26393 1.4224e+00 26350 1.42e+00 26269 1.01e-01 2.8892e-13 26393 7.0805e-03 26350
        SPECIES_em     1.1284e+00 26350 3.0000e+00 26306 1.86e+00 26350 6.32e-02 2.9907e+00 26350 3.0000e+00 26306
        SPECIES_gasses 3.8347e-12 26393 1.8716e+01 26350 1.86e+01 26350 1.01e-01 3.8016e-12 26393 9.3164e-02 26350
      * TEMPERATURE    3.0013e+02 26308 1.2000e+03 26818 4.57e+02 26278 1.92e-02 3.0013e+02 26308 1.2000e+03 26818

      Region::execute() time for The_Region: 7.35e-02 sec.
      Transient TimeBlock failed, step 120, time 1.1900e+02, time step 1.0000e+00
      ERROR: Missed Chemistry Deactivation.
      Retrying step with a time step size ratio of 0.655535