A C++ implement of nested loop with variable dimension

For real life computational research, multi-dimension problems kill our time.

Consider an N-dimension problem. We write some codes with N level loops.

A month later, M-dimension problems need to be solved. All you can do is to rewrite the codes.

To deal with this problem, I came up with this solution. Coordinates in such case can be stored in a vector object. A non-nested loop then can be used if the vector itself can loop over all dimensions.

The tool present here is a pure head file. Just include it in your source file, and it should work.

First thing you should notice is that the work based on the standard container vector. Learn more about vector class if you are not familiar with it.

In this work, mdindex class is implemented. To use this class, include the head file

#include "path/to/mdindex.h"

The method listed below:

mdindex(const std::vector <int> &max);

Set the integer in max as the largest number of each dimension. For example, you have

std::vector<int> max{3,4,5};

This means here we have a three-dimension problem where the number of discrete points in each dimension is 3, 4, or 5, respectively.

Then you can write

mdindex in(max);

to have a multi-dimension index object.

mdindex(const mdindex& rhs);

The make a copy of rhs.

mdindex::reset();

Set all the indices to 0

• ++ -- operators. To the next or previous one.
• += -= operators. Run more steps.

You should notice as we are using C++, the index runs from 0 to (max-1). If it runs out of range, a runtime error is thrown. However, I choose not stop the program for some reason. For example, you type

for(mdindex in(max); in.get()!=in.max(); ++i);

This will work, but at the last cycle, a warning will be thrown.

You can also use in.overflow() to find whether it is overflowed. It is safe only when this value equals 0!

mdindex::get();

returns the current overall index.

mdindex::get(unsigned int i);

returns the current ith dimension index.

mdindex::max();

returns the total number of possible combination.

mdindex::max(unsigned int i);

returns the max ith dimension index.