adding modalvector

[prayush]

Proposed changes

Types of changes:

• Bugfix
• New feature

Component:

• Code
• Documentation
• Build system
• Continuous integration

Code review checklist

• The PR passes all checks, including unit tests, clang-tidy and IWYU. For
  instructions on how to perform the CI checks locally refer to the Dev guide
  on the Travis CI.
• The code is documented and the documentation renders correctly. Run make doc
  to generate the documentation locally into BUILD_DIR/docs/html. Then open
  index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.

Further comments

[codecov-io]

Codecov Report

Merging #5 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           develop      #5   +/-   ##
=======================================
  Coverage     98.8%   98.8%           
=======================================
  Files          316     316           
  Lines        11351   11351           
=======================================
  Hits         11215   11215           
  Misses         136     136

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