Started Loss, done softmax, up to p.125

I've implemented alot of support functions that needs to be refactored, optimised and tested; mean.h, exponential.h, matdiv.h matsum.h matsubtract.h. Maybe we need to have a look at if matdiv/matmul should be in the same. Same with matadd/matsubtract and if some of it should be in matvec.h.

include/numerics/matsum.h

@@ -0,0 +1,39 @@
+#ifndef _matsum_n_
+#define _matsum_n_
+
+#include "./utils/vector.h"
+#include "./utils/matrix.h"
+#include "./core/omp_config.h"
+
+namespace numerics{
+	
+	template <typename T>
+	utils::Vector<T> matsum(utils::Matrix<T>& A, std::string method) {
+
+		utils::Vector<T> b;
+
+		if (method == "row"){
+			b.resize(A.cols(), T{0});
+			for (uint64_t i = 0; i < A.cols(); ++i){
+				for (uint64_t j = 0; j < A.rows(); ++j){
+					b[i] += A(j, i); 
+				}
+			}
+		}else if (method == "col"){
+			b.resize(A.rows(), T{0});
+
+			for (uint64_t i = 0; i < A.cols(); ++i){
+				for (uint64_t j = 0; j < A.rows(); ++j){
+					b[j] += A(j, i); 
+				}
+			}
+		}else{
+			throw std::runtime_error("matsum: choose sum by: 'row' or 'col'");
+		}
+		return b;
+	}
+
+
+} // namespace numerics
+
+#endif // _matadd_n_