PPMT() function should not asserts that rate is a positive number

[majermi4]

This is:

- [x] a bug report

What is the expected behavior?

In an native excel, the =PPMT (rate, per, nper, pv, [fv], [type]) function allows rate parameter to be a negative value.

What is the current behavior?

The changes added in this commit/line now trigger error when calculating value of the PPMT function when negative rate value is given to it.

I have to admit that I'm not an expert on what the PPMT function does and how it is meant to be used but we have a lot of excel files from experts in the financial industry and they seem to use a negative rate value in this function which now causes our app to crash.

My proposed solution is to simply remove that one line of validation which will make PHPOffice/PhpSpreadsheet behave consistently with native excel.

Which versions of PhpSpreadsheet and PHP are affected?

Effected PhpSpreadsheet version: 1.18.0 and higher

[MarkBaker]

There was a time when MS provided decent, consistent documentation on all of the Excel functions, not simply providing an example or two, but detailing all the validations, and the errors that would be returned. Sadly, that is no longer the case.

[PowerKiKi]

Fixed in 1.19.0