Task: Element-wise operations
C++: #include <cassert>
#include <cmath>
#include <iostream>
#include <valarray>

template <typename scalar_type> class matrix {
public:
    matrix(size_t rows, size_t columns) : rows_(rows), columns_(columns) {
        elements_.resize(rows * columns);
    }
    matrix(size_t rows, size_t columns, scalar_type value)
        : rows_(rows), columns_(columns), elements_(value, rows * columns) {}

    size_t rows() const { return rows_; }
    size_t columns() const { return columns_; }

    const scalar_type& at(size_t row, size_t column) const {
        assert(row < rows_);
        assert(column < columns_);
        return elements_[index(row, column)];
    }
    scalar_type& at(size_t row, size_t column) {
        assert(row < rows_);
        assert(column < columns_);
        return elements_[index(row, column)];
    }

    matrix& operator+=(scalar_type e) {
        elements_ += e;
        return *this;
    }
    matrix& operator-=(scalar_type e) {
        elements_ -= e;
        return *this;
    }
    matrix& operator*=(scalar_type e) {
        elements_ *= e;
        return *this;
    }
    matrix& operator/=(scalar_type e) {
        elements_ /= e;
        return *this;
    }

    matrix& operator+=(const matrix& other) {
        assert(rows_ == other.rows_);
        assert(columns_ == other.columns_);
        elements_ += other.elements_;
        return *this;
    }
    matrix& operator-=(const matrix& other) {
        assert(rows_ == other.rows_);
        assert(columns_ == other.columns_);
        elements_ -= other.elements_;
        return *this;
    }
    matrix& operator*=(const matrix& other) {
        assert(rows_ == other.rows_);
        assert(columns_ == other.columns_);
        elements_ *= other.elements_;
        return *this;
    }
    matrix& operator/=(const matrix& other) {
        assert(rows_ == other.rows_);
        assert(columns_ == other.columns_);
        elements_ /= other.elements_;
        return *this;
    }

    matrix& negate() {
        for (scalar_type& element : elements_)
            element = -element;
        return *this;
    }
    matrix& invert() {
        for (scalar_type& element : elements_)
            element = 1 / element;
        return *this;
    }

    friend matrix pow(const matrix& a, scalar_type b) {
        return matrix(a.rows_, a.columns_, std::pow(a.elements_, b));
    }
    friend matrix pow(const matrix& a, const matrix& b) {
        assert(a.rows_ == b.rows_);
        assert(a.columns_ == b.columns_);
        return matrix(a.rows_, a.columns_, std::pow(a.elements_, b.elements_));
    }
private:
    matrix(size_t rows, size_t columns, std::valarray<scalar_type>&& values)
        : rows_(rows), columns_(columns), elements_(std::move(values)) {}

    size_t index(size_t row, size_t column) const {
        return row * columns_ + column;
    }
    size_t rows_;
    size_t columns_;
    std::valarray<scalar_type> elements_;
};

template <typename scalar_type>
matrix<scalar_type> operator+(const matrix<scalar_type>& a, scalar_type b) {
    matrix<scalar_type> c(a);
    c += b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator-(const matrix<scalar_type>& a, scalar_type b) {
    matrix<scalar_type> c(a);
    c -= b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator*(const matrix<scalar_type>& a, scalar_type b) {
    matrix<scalar_type> c(a);
    c *= b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator/(const matrix<scalar_type>& a, scalar_type b) {
    matrix<scalar_type> c(a);
    c /= b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator+(scalar_type a, const matrix<scalar_type>& b) {
    matrix<scalar_type> c(b);
    c += a;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator-(scalar_type a, const matrix<scalar_type>& b) {
    matrix<scalar_type> c(b);
    c.negate() += a;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator*(scalar_type a, const matrix<scalar_type>& b) {
    matrix<scalar_type> c(b);
    c *= a;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator/(scalar_type a, const matrix<scalar_type>& b) {
    matrix<scalar_type> c(b);
    c.invert() *= a;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator+(const matrix<scalar_type>& a,
                              const matrix<scalar_type>& b) {
    matrix<scalar_type> c(a);
    c += b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator-(const matrix<scalar_type>& a,
                              const matrix<scalar_type>& b) {
    matrix<scalar_type> c(a);
    c -= b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator*(const matrix<scalar_type>& a,
                              const matrix<scalar_type>& b) {
    matrix<scalar_type> c(a);
    c *= b;
    return c;
}

template <typename scalar_type>
matrix<scalar_type> operator/(const matrix<scalar_type>& a,
                              const matrix<scalar_type>& b) {
    matrix<scalar_type> c(a);
    c /= b;
    return c;
}

template <typename scalar_type>
void print(std::ostream& out, const matrix<scalar_type>& matrix) {
    out << '[';
    size_t rows = matrix.rows(), columns = matrix.columns();
    for (size_t row = 0; row < rows; ++row) {
        if (row > 0)
            out << ", ";
        out << '[';
        for (size_t column = 0; column < columns; ++column) {
            if (column > 0)
                out << ", ";
            out << matrix.at(row, column);
        }
        out << ']';
    }
    out << "]\n";
}

void test_matrix_matrix() {
    const size_t rows = 3, columns = 2;
    matrix<double> a(rows, columns);
    for (size_t i = 0; i < rows; ++i) {
        for (size_t j = 0; j < columns; ++j)
            a.at(i, j) = double(columns * i + j + 1);
    }
    matrix<double> b(a);

    std::cout << "a + b:\n";
    print(std::cout, a + b);

    std::cout << "\na - b:\n";
    print(std::cout, a - b);

    std::cout << "\na * b:\n";
    print(std::cout, a * b);

    std::cout << "\na / b:\n";
    print(std::cout, a / b);

    std::cout << "\npow(a, b):\n";
    print(std::cout, pow(a, b));
}

void test_matrix_scalar() {
    const size_t rows = 3, columns = 4;
    matrix<double> a(rows, columns);
    for (size_t i = 0; i < rows; ++i) {
        for (size_t j = 0; j < columns; ++j)
            a.at(i, j) = double(columns * i + j + 1);
    }

    std::cout << "a + 10:\n";
    print(std::cout, a + 10.0);

    std::cout << "\na - 10:\n";
    print(std::cout, a - 10.0);

    std::cout << "\n10 - a:\n";
    print(std::cout, 10.0 - a);

    std::cout << "\na * 10:\n";
    print(std::cout, a * 10.0);

    std::cout << "\na / 10:\n";
    print(std::cout, a / 10.0);

    std::cout << "\npow(a, 0.5):\n";
    print(std::cout, pow(a, 0.5));
}

int main() {
    test_matrix_matrix();
    std::cout << '\n';
    test_matrix_scalar();
    return 0;
}

Java: import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;
import java.util.stream.Stream;

@SuppressWarnings("serial")
public class ElementWiseOp {
	static final Map<String, BiFunction<Double, Double, Double>> OPERATIONS = new HashMap<String, BiFunction<Double, Double, Double>>() {
		{
			put("add", (a, b) -> a + b);
			put("sub", (a, b) -> a - b);
			put("mul", (a, b) -> a * b);
			put("div", (a, b) -> a / b);
			put("pow", (a, b) -> Math.pow(a, b));
			put("mod", (a, b) -> a % b);
		}
	};
	public static Double[][] scalarOp(String op, Double[][] matr, Double scalar) {
		BiFunction<Double, Double, Double> operation = OPERATIONS.getOrDefault(op, (a, b) -> a);
		Double[][] result = new Double[matr.length][matr[0].length];
		for (int i = 0; i < matr.length; i++) {
			for (int j = 0; j < matr[i].length; j++) {
				result[i][j] = operation.apply(matr[i][j], scalar);
			}
		}
		return result;
	}
	public static Double[][] matrOp(String op, Double[][] matr, Double[][] scalar) {
		BiFunction<Double, Double, Double> operation = OPERATIONS.getOrDefault(op, (a, b) -> a);
		Double[][] result = new Double[matr.length][Stream.of(matr).mapToInt(a -> a.length).max().getAsInt()];
		for (int i = 0; i < matr.length; i++) {
			for (int j = 0; j < matr[i].length; j++) {
				result[i][j] = operation.apply(matr[i][j], scalar[i % scalar.length][j
						% scalar[i % scalar.length].length]);
			}
		}
		return result;
	}
	public static void printMatrix(Double[][] matr) {
		Stream.of(matr).map(Arrays::toString).forEach(System.out::println);
	}
	public static void main(String[] args) {
		printMatrix(scalarOp("mul", new Double[][] {
				{ 1.0, 2.0, 3.0 }, 
				{ 4.0, 5.0, 6.0 }, 
				{ 7.0, 8.0, 9.0 }
		}, 3.0));

		printMatrix(matrOp("div", new Double[][] {
				{ 1.0, 2.0, 3.0 }, 
				{ 4.0, 5.0, 6.0 }, 
				{ 7.0, 8.0, 9.0 }
		}, new Double[][] {
				{ 1.0, 2.0}, 
				{ 3.0, 4.0} 
		}));
	}
}