4.1.5. Inversion Program

Both the forward and inverse problems are solved using the e3d.exe executable program. In each case, format of the input file (denoted here as e3dinv.inp) is the same. In the case of forward modeling however, some lines in the input file are omitted.

4.1.5.1. Running the Program

Here, the mpiexec call is used to parallelize multiple processes (large-scale independent operations) within the code. To run the executable, open a command window and type the following:

../../_images/run_e3dinv.png

The call mpiexec is followed by the flag -n, then the number of processes (“nFreq” ) to be carried out simultaneously. This is followed by the paths to the executable and the corresponding input file, respectively. The number of simultaneous processes (“nFreq” ) must be equal or less than the number of frequencies. Ideally there is enough memory for nFreq to be equal to the number of frequencies.

4.1.5.2. Setting Number of Threads with Open MPI

Before running the executable, the number of threads used to carry out all simultaneous processes can be set with Open MPI. This is set in the command window before running the executable. To set the number of threads (nThreads ), use the following syntax:

  • Windows computer: “set OMP_NUM_THREADS=nThreads”

  • Linux (bash shell): “export OMP_NUM_THREADS=nThreads”

  • Linux (csh shell): “setenv OMP_NUM_THREADS nThreads”

Important

The number of processes (nFreq ) times the number of threads (nThreads ) cannot exceed the total number of threads available from the computer.

4.1.5.3. Units

  • Electric field data: Real and imaginary components of Ex, Ey and Ez in units V/m

  • Magnetic field data: Real and imaginary components of the total magnetic field or secondary magnetic field Hx, Hy and Hz in units A/m.

  • Conductivity model: S/m

  • Reference/starting conductivity model: S/m

  • Model/interface weights: unitless

Important

Any combination of data, electric and or magnetic field components, can be be inverted. A specified flag at the start of the observations file can be used to omit columns or individual datums.

4.1.5.4. Output Files

The program e3d.exe creates the following output files:

  • dpred_fwd.txt predicted data if forward modeling is used

  • model0.con: the starting model

  • dpred0.txt data predicted using the starting model

  • inv_xx.con: recovered model at iteration ‘xx’

  • dpred_xx.txt data predicted using model ‘xx’

  • inv.con: final conductivity model

  • e3d.log: log file for the inversion

  • e3d.out: stores details regarding the inversion