What is the "const gsl_vector_float" required by GSL BLAS functions?

Question

I am trying to use GSL to compute the dot product between two vectors. The vectors are views of the columns of a matrix. I call the function like gsl_blas_dsdot( &view1.vector, &view2.vector, &val), but upon compilation I get warnings stating that the function expected argument types const gsl_vector_float *, and I get a nonsensical result. Here is a code to demonstrate:

#include<stdio.h>
#include<gsl/gsl_matrix.h>
#include<gsl/gsl_vector.h>
#include<gsl/gsl_blas.h>

void main(void){
  int i;
  double val = 111.111; // Initialize to something
  gsl_matrix *A = gsl_matrix_alloc(3,3); //Initialize mx
  gsl_matrix_set_identity(A);  // Set mx to identity
  gsl_matrix_set(A,0,1,3.14);
  gsl_vector_view a1 = gsl_matrix_column(A,0); // Vector allocations
  gsl_vector_view a2 = gsl_matrix_column(A,1);
  /* Print the vectors */
  printf("a1 = ");
  for(i=0; i<3; i++){
    printf("%g ", gsl_vector_get(&a1.vector,i));}
  printf("\na2 = ");
  for(i=0; i<3; i++){
    printf("%g ", gsl_vector_get(&a2.vector,i));}
  printf("\n");
  gsl_blas_dsdot(&a1.vector, &a2.vector, &val); // Dot product 
  printf("a1.a2 = %.2f\n", val);  // Print result
}

I compile with gcc version 5.4.0, GSL version 2.2.1, with the following:

gcc example.c -o example -lgsl -lgslcblas

And I get the following warnings, and though the program executes, the result is nonsensical:

gsl_dot.c: In function ‘main’:
gsl_dot.c:22:18: warning: passing argument 1 of ‘gsl_blas_dsdot’ from incompatible pointer type [-Wincompatible-pointer-types]
   gsl_blas_dsdot(&a1.vector, &a2.vector, &val); // Dot product 
                  ^
In file included from gsl_dot.c:4:0:
/usr/local/include/gsl/gsl_blas.h:56:5: note: expected ‘const gsl_vector_float * {aka const struct <anonymous> *}’ but argument is of type ‘gsl_vector * {aka struct <anonymous> *}’
 int gsl_blas_dsdot (const gsl_vector_float * X,
     ^
gsl_dot.c:22:30: warning: passing argument 2 of ‘gsl_blas_dsdot’ from incompatible pointer type [-Wincompatible-pointer-types]
   gsl_blas_dsdot(&a1.vector, &a2.vector, &val); // Dot product 
                              ^
In file included from gsl_dot.c:4:0:
/usr/local/include/gsl/gsl_blas.h:56:5: note: expected ‘const gsl_vector_float * {aka const struct <anonymous> *}’ but argument is of type ‘gsl_vector * {aka struct <anonymous> *}’
 int gsl_blas_dsdot (const gsl_vector_float * 

Note also that copying the matrix columns into gsl_vector types using get_matrix_get_col() results in the same warnings.

Can anyone please assist? What is it about these gsl vectors and vector views that make them an incompatible type? What are these const gsl_vector_float types?

Answer 1

I still don't know what a const gsl_vector_float is, but I did figure out that using the function gsl_blas_ddot instead of gsl_blas_dsdot compiles without warnings and executes correctly.

According to the documentation, which I wish gave more detail, gsl_blas_ddot takes const gsl_vector * as argument. This is apparently different from the const gsl_vector_float * in question.