add discretization of cost and covariance matrices

[baggepinnen]

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Plots were compared to references. 11/11 images have changed, see differences below.
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[codecov]

Codecov Report

Merging #862 (92010a5) into master (7407550) will increase coverage by 1.51%.
The diff coverage is n/a.

❗ Current head 92010a5 differs from pull request most recent head e6a7844. Consider uploading reports for the commit e6a7844 to get more accurate results

@@            Coverage Diff             @@
##           master     #862      +/-   ##
==========================================
+ Coverage   91.21%   92.72%   +1.51%     
==========================================
  Files           5        5              
  Lines         330      330              
==========================================
+ Hits          301      306       +5     
+ Misses         29       24       -5     

see 1 file with indirect coverage changes