Fixed coherence calculation

[rosali2003]

Description

There was a mistake in the previous calculation of coherence values. A low range in heart rate values should correspond to a high coherence value therefore I re-calculated the coherence value as follow:

• find the range of heart rate values in a 5 second interval
• find the 'factor' which is the range divided by 3
• divide the range by 6 and subtract from the factor Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Type of change

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• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

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• [x] Test A
• [ ] Test B

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Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

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