qrSolve

import mir.ndslice;

auto A =
        [ 3,  1, -1,  2,
         -5,  1,  3, -4,
          2,  0,  1, -1,
          1, -5,  3, -3 ]
          .sliced(4, 4)
          .as!double.slice;

import mir.random.variable;
import mir.random.algorithm;
auto B = randomSlice(uniformVar(-100, 100), 4, 100);

auto C = qrDecomp(A);
auto X = C.solve(B);

import mir.math.common: approxEqual;
import mir.algorithm.iteration: equal;
alias appr = equal!((a, b) => approxEqual(a, b, 1e-5, 1e-5));
assert(appr(mtimes(A, X), B));