docs: public double[][] solve(double[][] B) {
      if(B.length != L.length) {
        throw new IllegalArgumentException(ERR_MATRIX_DIMENSIONS);
      }
      if(!isspd) {
        throw new ArithmeticException(ERR_MATRIX_NOT_SPD);
      }
      // Work on a copy!
      return solveLtransposed(solveL(copy(B)));
    }