Minkoo Seo wrote:

Hi list.

I got a problem of matrix initialization. Please see the following code:

#include <iostream> #include <iterator> #include #include

using namespace std; using namespace boost::numeric::ublas;

int main () { matrix<double> m(3, 3); for (unsigned i = 0; i < 3; i++) m(i, i) = -i;

cout << m << endl;

return EXIT_SUCCESS; }

In this code, I'm trying to initialize the diagonal with -1, -2, -3. But, the result is obviously different from what I expected:

[3,3]((0,0,0),(0,4.29497e+09,0),(0,0,4.29497e+09))

This must be due to type conversion from unsigned from double that occurs at 'm(i, i) = -i'. IMHO, the code must works as follows

i // unsigned -i // (-1) * i = int * unsigned = int m(i, i) = -i // lhs is double, so int on rhs should be converted // into double.

But the result implies that I'm wrong. Anybody knows what I'm missing here?

You are missing that C++ promotion rules are very weird. int * unsigned = unsigned.

How would you correct the above code?

Don't use unsigned, and especially, don't mix them with signed types. Cheers, Ian