Matrix sum along a dimension is defined to return a MathScalarType, but might return higher dimension

[itaiperi]

Describe the bug
When summing over an axis of a matrix, we always lose just one dimension. If the matrix is 2D, we'll get a 1D array. If the matrix is 3D, we'll get a 2D matrix.
What happens now, is that math.sum declares that it returns a MathScalarType, instead of optionally returning a matrix.

To Reproduce

const mat = math.matrix([[1,2,3],[4,5,6]])
console.log(math.sum(mat, 0))

> DenseMatrix { _data: [ 5, 7, 9 ], _size: [ 3 ], _datatype: undefined }

[josdejong]

Thanks for reporting Itai.

We have to fix the TypeScript type definitions for sum (and check functions like prod to see if there are similar issues there).

Anyone able to help with a PR fixing the types?

[deflucaseng]

Could I get assigned to this?

[josdejong]

Thanks @deflucaseng, I've assigned you for this task.

[deflucaseng]

@josdejong I also saw that deepForEach.test.js was left as TODO. Is that something I can also work on?

[josdejong]

Definitely! Thanks Lucas. Can you please create two separate PR's, so each addresses 1 thing?