= 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.