Write your own code and run it as a test

Next: A 2-D Modeling experiment Up: Forward modeling Previous: Forward modeling

Write your own code and run it as a test

You have to

create a user directory in /RSFSRC/user/dirname, where dirname is the directory name, for example, 'pyang'.
copy a SConstruct from other existing users, and use it as a template to create your own things. For example, take /RSFSRC/user/psava/SConstruct. Assume you are going to do C programming to generate a target executable sfmodeling2d. You need to empty all other code list while add a name in C code list: $\begin{lstlisting} import os, systry: import bldutil glob_build = True ...$
Use text editor (emacs, gedit, ...) to create a file Mmodeling2d.c (which will generate the target sfmodeling2d, M will be automatically replaced by sf). In Mmodeling2d.c, start your codes by including the RSF header file: #include <rsf.h>, which defines many useful interfaces/subroutines for the convenience of data I/O (including parameters and files)
```
  sf_input()/sf_output()
  sf_histint()/sf_histfloat()
  sf_getint()/sf_getfloat()
```
and memory allocation for the variables
```
  
  sf_intalloc()/sf_floatalloc()
  sf_intalloc2()/sf_floatalloc2()
  ...
```
which will be used frequently when coding with Madagascar.
specify your input and output files, and initialize Madagascar:
$\begin{lstlisting} sf_file vinit, shots; /* input and output file*/ sf_init(arg... ... model in m/s */ shots=sf_output(''out''); /* output image */ \end{lstlisting}$ Here the input file vinit is the velocity model, while the output shots is a shot gather (or many shots) collected at many receivers for different sources.
read the parameters from the input file using the interfaces Madagascar prepared: sf_hist*(),sf_get*() $\begin{lstlisting} /* get parameters for forward modeling */ if (!sf_histint(vin... ... /* default, common shot-gather; if n, record at every point*/ \end{lstlisting}$
specify the parameters for the output file using the interfaces Madagascar prepared: sf_put*() $\begin{lstlisting} /* put the labels, legends and parameters in output */ sf_put... ...ts,''jgz'',jgz); sf_putint(shots,''csdgather'',csdgather?1:0); \end{lstlisting}$
allocate memory for the arries, format: sf_floatalloc2(n1,n2) $\begin{lstlisting} /* allocate the variables */ wlt=(float*)malloc(nt*sizeof(flo... ...int*)malloc(ns*sizeof(int)); gxz=(int*)malloc(ng*sizeof(int)); \end{lstlisting}$
do your own computation (forward simulation) as usual. The whole time stepping looks like $\begin{lstlisting} memset(p0[0],0,nz*nx*sizeof(float)); memset(p1[0],0,nz*nx*s... ...1=p2; p2=ptr; record_seis(&dobs[it*ng], gxz, p0, ng, nz); } \end{lstlisting}$
free the variables $\begin{lstlisting} /* free the variables */ free(sxz); free(gxz); free(bndr); fr... ...free(*p0); free(p0); free(*p1); free(p1); free(*p2); free(p2);\end{lstlisting}$
Finally, you end up with a complete code /RSFSRC/user/pyang/Mmodeling2d.c. You can go into directory RSFSRC, compile and install the target executable sfmodeling2d:
```
   cd $RSFSRC
   scons install
```
If there exists any error in your code, you will get the reporting message in the terminal.

Next: A 2-D Modeling experiment Up: Forward modeling Previous: Forward modeling

2021-08-31