gsl_vector_fprintf

["E. Robert Tisdale" <edwin at netwood dot net>]

I am suggesting that the GSL vector fprintf function be changed from

    int gsl_vector_fprintf(FILE *stream, const gsl_vector* v,
      const char* format);

to

    int gsl_vector_fprintf(FILE *stream, const gsl_vector* v,
      int width, unsigned int precision, unsigned int columns);

This permits the numerical application programmer
to display columns elements of a row vector at a time
on a line with a space between each element on a line
like this:

    0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

instead of like this:

    0.0
    1.0
    2.0
    3.0
    4.0
    5.0
    6.0
    7.0
    8.0
    9.0

for a vector of 10 elements, for example.
A similar function for type gsl_matrix
simply prints the row vectors in order
so that it appears as a matrix on the display
if all of the columns of a row fit on one line.

int gsl_fprintf(FILE *stream, gsl_double x,
  int width, unsigned int precision) {
  char format[64];
  int   characters = sprintf(format, "%%%d.%ue", width, precision);
  if (0 <= characters) {
    return fprintf(stream, format, (gsl_double)x); } else { return -1; }
  }

int gsl_vector_fprintf(FILE *stream, const gsl_vector* v,
  int width, unsigned int precision, unsigned int columns) {
  int           modulus = (0 < columns)? columns: 4;
  int           characters;
  int           total = 0;
  gsl_extent    n = gsl_vector_extent(v);
  gsl_offset    j = 0;
  for (j = 0; j < n; j++) {
    characters = (0 == j%modulus)? fprintf(stream, "\n"): fprintf(stream, " ");
    if (0 <= characters) { total += characters; } else { return -1; }
    characters = gsl_fprintf(stream, gsl_vector_get(v, j), width, precision);
    if (0 <= characters) { total += characters; } else { return -1; }
    }
  characters = fprintf(stream, "\n");
  if (0 <= characters) { total += characters; } else { return -1; }
  return total;
  }