4.1.5. Inversion Program

Both the forward and inverse problems are solved using the e3d_v2.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_ver2.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

  • Magnetic field data: the component of the total magnetic field or secondary field along the direction of the receiver’s dipole moment in units A/m

  • Electric field data: the component of the electric field along the path of the wire segment

  • Conductivity model: S/m

  • Reference/starting conductivity model: S/m

  • Model/interface weights: unitless

Important

  • If a flag value of -99 is used as the uncertainty for a particular datum, the inversion will omit that datum. Using this, we are not required to invert all of the data.

4.1.5.4. Output Files

The program e3d_v2.exe creates the following output files:

  • inv.con: recovered conductivity model for the final beta value

  • inv_xxx.con: recovered conductivity model for the nth beta value

  • dpred0.txt predicted data for the initial model

  • dpred_xxx.txt predicted data for the nth beta value

  • dpred.txt predicted data for final recovered model

  • e3d_v2.log: log file for the inversion

  • e3d_v2.out: inversion summary