Often times people state that Degrees of Freedom are a good indicator in how long it will take to solve a solution. I'm running a bunch of simple tests (comparing different solid elements) and i'm trying to find information in the .log, .f04, or .f06 files that I can compare across different analyses to see how computationaly intensive each one is. I know that the .log file states the number of degrees of freedom at the end, however I don't find that this is detailed enough. You get the same DOF for a solution using Reduced integration elements as you do Full integration elements (which makes sense). Is there information that shows that number of integration points, size of the stiffness matrix, etc? I want something that can be used to compare my solution accuracy to their size (previous I was using DOF).
For a linear solution, decomp will typically be the most expensive step. Detailed information for this can be found in the .f04 file.
If you are running with the default sparse solver, look for the DCMP (DeCoMP) module output. It will document the information you are looking for, i.e.:
9:22:51 0:00 981.0 0.0 0.3 0.0 SEKRRS 186 DCMP BEGN *** USER INFORMATION MESSAGE 4157 (DFMSYN) PARAMETERS FOR PARALLEL SPARSE DECOMPOSITION OF DATA BLOCK KLL ( TYPE=RSP ) FOLLOW MATRIX SIZE = 1728 ROWS NUMBER OF NONZEROES = 14850 TERMS NUMBER OF ZERO COLUMNS = 0 NUMBER OF ZERO DIAGONAL TERMS = 0 SYSTEM (107) = 32770 REQUESTED PROC. = 2 CPUS User information: When spill is indicated, the model is too large to fit into memory. The job may run faster by increasing the available memory (this will decrease the number of spill groups). See the NASTRAN Installation and Operation Instructions for a description of these terms. See also the NASTRAN Numerical Methods User's Guide. CPU TIME ESTIMATE = 0 SEC I/O TIME ESTIMATE = 0 SEC MINIMUM MEMORY REQUIREMENT = 1488 KB MEMORY AVAILABLE = 9012944 KB MEMORY REQR'D TO AVOID SPILL = 2520 KB MEMORY USED BY MMD = 96 KB EST. INTEGER WORDS IN FACTOR = 26 K WORDS EST. NONZERO TERMS = 54 K TERMS ESTIMATED MAXIMUM FRONT SIZE = 60 TERMS RANK OF UPDATE = 128 *** USER INFORMATION MESSAGE 6439 (DFMSA) ACTUAL MEMORY AND DISK SPACE REQUIREMENTS FOR SPARSE SYM. DECOMPOSITION User information: This message is issued in the .F04 file after decomposition. It tells how much memory and desk space were actually required. SPARSE DECOMP MEMORY USED = 2520 KB MAXIMUM FRONT SIZE = 60 TERMS INTEGER WORDS IN FACTOR = 5 K WORDS NONZERO TERMS IN FACTOR = 54 K TERMS SPARSE DECOMP SUGGESTED MEMORY = 2520 KB *8** Module DMAP Matrix Cols Rows F T IBlks NBlks NumFrt FrtMax DCMP 186 LLL 1728 1728 13 1 1 2 154 60 *8** *8** Module DMAP Matrix Cols Rows F T NzWds Density BlockT StrL NbrStr BndAvg BndMax NulCol DCMP 186 SCR 301 1 1728 2 1 1728 1.00000E+00 3 1728 1 1728 1728 0 *8** DCMP 186 SCR 302 1 1728 2 1 1728 1.00000E+00 3 1728 1 1728 1728 0 *8** 9:22:51 0:00 981.0 0.0 0.3 0.0 SEKRRS 186 DCMP END
Some notes on the above output:
Other solvers (i.e. Pardiso, element iterative) or solutions (i.e. eigenvalue) will print similar information to the .f04. The format is specific to the solver/solution sequence.
For iterative or nonlinear solutions, matrix decomp is not necessarily the best indicator of solution time. Number of iterations/time steps/bisections typically dictate overall time, but these are unknown prior to solving.
There are lot of additional features that can affect analysis time on same model: SOL type (linear/nonlinear), number of steps/frequencies in nonlinear/transient/modal/frequency response analysis, contact regions/contact search distance, nonlinear material, some Nonlinear solvers can split load step to achieve solution so number if iterations may be different due to convergence problems.
Therefore, I think that trying to predict solution time is useless exercise. Juts use your experience and common sense not to get unacceptable solution time.