added readme and results from our machine

p1afempy/tests/data/matlab_performance/stiffness_matrix_assembly/means.dat

@@ -0,0 +1,11 @@
+   1.0000000e-03
+   0.0000000e+00
+   0.0000000e+00
+   0.0000000e+00
+   5.0000000e-04
+   4.5000000e-03
+   7.0000000e-03
+   2.1500000e-02
+   9.8500000e-02
+   8.6050000e-01
+   4.4650000e+00

p1afempy/tests/data/matlab_performance/stiffness_matrix_assembly/n_elements.dat

@@ -0,0 +1,11 @@
+   2.0000000e+00
+   8.0000000e+00
+   3.2000000e+01
+   1.2800000e+02
+   5.1200000e+02
+   2.0480000e+03
+   8.1920000e+03
+   3.2768000e+04
+   1.3107200e+05
+   5.2428800e+05
+   2.0971520e+06

p1afempy/tests/data/matlab_performance/stiffness_matrix_assembly/readme.md

@@ -0,0 +1,24 @@
+# Performance Test: Stiffness Matrix Assembly
+
+In this directory, you can find everything needed to perform
+a performance test on the Matlab implementation of the stiffness matrix
+assembly.
+For completeness' sake (e.g. if you do not posess a Matlab license),
+we added test results found on our machine,
+whose specs can be found below.
+
+| **Device**       | MacBook Pro 15-inch, 2018       |
+|-------------------|---------------------------------|
+| **Processor**    | 2.6 GHz 6-Core Intel Core i7    |
+| **Graphics**     | Radeon Pro 560X 4 GB            |
+|                  | Intel UHD Graphics 630 1536 MB |
+| **Memory**       | 16 GB 2400 MHz DDR4             |
+| **Operating System** | MacOS 13.6.3 (22G436)         |
+| **Matlab Version**   | R2023b                          |
+
+
+
+## Setup
+The test case considered is a simple unit square.
+In each refinement step, we refine the mesh using `RefineNVB`,
+where all elements are marked for refinement.

p1afempy/tests/data/matlab_performance/stiffness_matrix_assembly/stdevs.dat

@@ -0,0 +1,11 @@
+   3.0779351e-03
+   0.0000000e+00
+   0.0000000e+00
+   0.0000000e+00
+   2.2360680e-03
+   6.0480532e-03
+   8.6450473e-03
+   5.8714295e-03
+   1.5312534e-02
+   5.7443336e-02
+   1.2458352e-01