# Boost :

From: Benedikt Weber (weber_at_[hidden])
Date: 2002-07-01 10:26:02

ublas is very flexible when combining matrices of different shapes. However,
some type safety would sometimes be useful. When initializing a triangular
matrix by a full matrix, there is no compiler error. At runtime, the
triangular matrix just takes what it needs, without giving a warning. With
assignment it's the same problem. There are macros NUMERICS_USE_FAST_COMMON
and NUMERICS_BOUNDS_CHECK which I tried to undefine, to get a bound check,
but I see no difference in the behaviour.

#undef NUMERICS_USE_FAST_COMMON
#undef NUMERICS_BOUNDS_CHECK

const n= 3;
numerics::matrix<double> A(n,n);
for (int i= 0; i<n; ++i)
for (int j= 0; j<n; ++j)
A(i,j)= i+j;

std::cout << "A" << std::endl;
std::cout << A << std::endl;

try {
numerics::triangular_matrix<double> B= A; // undetected
std::cout << "B= A" << std::endl;
std::cout << B << std::endl;
}
catch (std::exception& e) {
std::cout << e.what() << std::endl;
}
catch (...) {
std::cout << "unknown exception" << std::endl;
}

A
[3,3]((0,1,2),(1,2,3),(2,3,4))
B= A
[3,3]((0,0,0),(1,2,0),(2,3,4))

Another example is assigning a larger to a smaller matrix. The problems are
the same ones as before.

try {
numerics::matrix<double> B(n-1,n-1);
B.assign(A); // undetecetd
std::cout << "B.assign(A)" << std::endl;
std::cout << B << std::endl;
}
catch (std::exception& e) {
std::cout << e.what() << std::endl;
}
catch (...) {
std::cout << "unknown exception" << std::endl;
}

B.assign(A)
[2,2]((0,1),(1,2))

I am a little bit concerned, that you can do all these errors without
getting warned! Is there something I missed or is just that way with
expression templates? What are these macros good for?

Benedikt