adjoint function
Calculates the adjugate of a mat2
@param {mat2} out the receiving matrix @param {ReadonlyMat2} a the source matrix @returns {mat2} out
Implementation
adjoint(List<double> out, List<double> a) {
// Caching this value is necessary if out == a
final a0 = a[0];
out[0] = a[3];
out[1] = -a[1];
out[2] = -a[2];
out[3] = a0;
return out;
}