fixed bug that leads to 1D linear material not behaving properly in simulations

[JRao-rgb]

Current situation

#110
I found out the linear material model is broken when I was testing the backwards compatibility of the leaky vessels code with previous sv input files. I initially thought it was my code that was broken, but the code just didn't handle linear materials properly.

Release Notes

• Changed the following functions in cvOneDMaterialLinear.cxx: GetArea(), GetPressure(), GetDpDS(). Not sure how the previous maintainer arrived at these forms, but they differ a lot from the implementation in cvOneDMaterialOlufsen.cxx, which doesn't make much sense (since the two models are only different in the EHR computation).
• Changed the function GetN() in cvOneDMaterialLinear.h from "return 0.0;" to "return N;".
• Added relevant test cases so that the linear material can be tested when future versions of the code are changed.

Documentation

• Just a bug fix.

Testing

Please ensure that the PR meets the testing requirements set by GitHub Actions.

• See above for testing results. The linear material should undergo tests now.

Code of Conduct & Contributing Guidelines

• I agree to follow the Code of Conduct and Contributing Guidelines.

[JRao-rgb]

@mrp089 should be good to merge! Please take a look when you get time.

[mrp089]

Thank you so much for doing this, @JRao-rgb! Please see my comments and ask me if you have any questions. Congratulations on your first pull request!

[mrp089]

Check out this file from master branch because there are only formatting changes in here

[mrp089]

Would it make sense to do one of these tests with " $Eh/r \ll\infty$ " for Olufsen and Linear material? Then, we should see that they deform similarly. Currently, So_/S would always be close to one, right?

[mrp089]

No need to add date and initials (even though people did it before), that's now all stored in git. You can check it out by doing a git blame on a file.