#ifndef TRANSFORMMATRIX_H
#define TRANSFORMMATRIX_H
#include "matrix.h"
#include "math.h"

class BaseTransformMatrix : public Matrix<double>
{
public:
    BaseTransformMatrix();
};

class MoveMatrix : public BaseTransformMatrix
{
public:
    MoveMatrix(double x, double y, double z);
};

#endif // TRANSFORMMATRIX_H

#ifndef MATRIX_H
#define MATRIX_H
#include "vector.h"
#include "base_matrix.h"

template <typename T>
class Matrix : public BaseMatrix
{
public:
    Matrix();
    Matrix(int m, int n);
    ... // Other methods and fields

private:
    Vector<Vector<T>> matr;
};

#include "matrix.cpp" // Файл реализации с методами
#endif // MATRIX_H

#ifndef BASE_MATRIX_H
#define BASE_MATRIX_H

class BaseMatrix
{
protected:
    int m;
    int n;

public:
    BaseMatrix();
    BaseMatrix(int m, int n);
    BaseMatrix(const BaseMatrix &matrix) = delete;

    virtual ~BaseMatrix() {}

    int length_m() const;
    int length_n() const;
    bool isEmpty() const;
};

#include "base_matrix.cpp" // Опять же файл реализации

#endif // BASE_MATRIX_H

#ifndef BASE_MATRIX_CPP
#define BASE_MATRIX_CPP
#include "base_matrix.h"

BaseMatrix::BaseMatrix():m(0), n(0) {}

BaseMatrix::BaseMatrix(int m, int n):m(m), n(n) {}

int BaseMatrix::length_m() const
{
    return this->m;
}

int BaseMatrix::length_n() const
{
    return this->n;
}

bool BaseMatrix::isEmpty() const
{
    if (this->m && this->n)
        return false;
    else
        return true;
}

#endif // BASE_MATRIX_CPP

...myTestbase_matrix.cpp:11: ошибка: multiple definition of `BaseMatrix::length_m() const'
...myTestbase_matrix.cpp:11: first defined here ...myTestbase_matrix.cpp
...myTestbase_matrix.cpp:17: ошибка: multiple definition of `BaseMatrix::length_n() const'
...

int main(){}