Add ipow function

[mborland]

Closes: #398

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.33%. Comparing base (ae034fd) to head (ad18eb3).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #405      +/-   ##
===========================================
+ Coverage    96.26%   96.33%   +0.06%     
===========================================
  Files           74       75       +1     
  Lines         6419     6541     +122     
  Branches      2166     2231      +65     
===========================================
+ Hits          6179     6301     +122     
  Misses          34       34              
  Partials       206      206              

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