Changes between Initial Version and Version 1 of cypress/Programming/FortranCpp

Timestamp:

05/15/15 11:55:47 (9 years ago)

Author:

cmaggio

Comment:

migrated content from ccs wiki

cypress/Programming/FortranCpp

@@ +1 @@
+= Fortran and C/C++ = 
+[[cypress/Programming/BlasLapack|BLAS / LAPACK]] routines are written in Fortran 77.
+
+Difference between C and Fortran:
+* The way matrices are stored in memory
+  * we have to transpose our matrices before we can pass them to a Fortran routine.
+* The way arguments are passed to a subroutine.
+  * In Fortran the argument is passed to the routine and the routine can read and change this value. (call by reference)
+  * In C a copy of the value of the argument is passed to the routine and not the argument itself, the subroutine can't change the value of the argument. (call by value)
+  * To use call by reference in C, we have to pass pointers to variables instead of the variables themselves to the routine.
+
+== Arrays in Fortran / C == 
+2D array (matrix) in C is defined as
+{{{#!c
+double matrix[10][10];
+}}}
+
+In Fortran,
+{{{#!fortran
+Real*8 matrix(10,10)
+}}}
+
+These 2D-array(matrix) are allocated in the 1D-memory (RAM) address space, however, the way of this is deferent in C and Fortran.
+
+In C,
+
+2D Array C.png
+
+In Fortran
+
+2D Array Fortran.png
+
+== How arguments passed in Fortran / C ==
+Subroutine Arg.png
+
+In Fortran, if make a value change in subroutine, the value in the main routine changes.
+
+To do 'call by reference' in C, send pointers.
+
+{{{#!c
+mysub(&a,&b,&c);
+
+:
+
+}
+
+void mybud(double *x,double *y,double *z){
+
+:
+
+}
+}}}
+
+== Fortran subroutine names from C ==
+Lower case, put “_” in end.
+
+For example, fortran subroutine
+
+{{{DNRM2(n,x,m,nm)}}}
+
+is :
+
+{{{dnrm2_(&n,x,&m,&nm);}}}
+
+when calling from C program.