“候选模板被忽略：替换失败”错误帮助，C ++，犰狳，rank（），

Question

I was playing around with the C++ armadillo library without doing anything serious. However, I'm getting an error I don't know to handle. I'm only passingly familiar with c++, and I really don't know where to begin. Anyway here's my code, it's really simple, it just makes an nxn matrix from 1-6 , fills it up from 1 to n^2, and then (attempts to) print the rank:

#include <iostream>
#include <armadillo>
#include <string>

using std::cout;
using std::to_string;
using std::string;
using namespace arma;


int main(int argc, char *argv[])
{
    int x = 1;
    int m,n = 0;

    for (int i=1; i<7; i++)
    {
        umat M(i,i);

        for (m=0; m<i; m++)
        {
            for (n=0; n<i; n++)
            {
                M(m,n) = (x+n+(i*m));
            }
        }

        string s = "M(" + to_string(i) + "x" + to_string(i) + "):";
        M.print(s);
        uword r = rank(M);
        cout << "rank(M): " << to_string( r )  << "\n";
        cout << "\n";
    }

    return (0);
}

My terminal in/output is:

$ g++ -o matrix matrix.cpp -larmadillo
matrix.cpp:35:13: error: no matching function for call to 'rank'
                uword r = rank(M);
                          ^~~~
/usr/local/include/armadillo_bits/fn_rank.hpp:22:1: note: candidate template ignored: substitution
      failure [with T1 = arma::Mat<unsigned int>]: no type named 'result' in
      'arma::arma_blas_type_only<unsigned int>'
rank
^ 1 error generated.

Answer 1

According to the documentation for the Mat class , the rank() function only works for matrices which have elements of type float , double , std::complex<float> , std::complex<double> .

The umat matrix type stores elements as unsigned integers. (The width of the integers is dependent on whether your OS is 32 or 64 bit and whether the compiler is using the old C++98 standard or the newer C++11 standard; see here ).

So to get your code working, change umat to mat . In other words, instead of umat M(i,i); use mat M(i,i);

If you really need to store data as integers in a umat , use the conv_to() function to convert the matrix before passing it to the rank() function:

double r = rank( conv_to<mat>::from(M) );