Instructions to run the example app

Given the screenshot on the original author's lab website
(https://www.ee.cuhk.edu.hk/~tblu/monsite/phps/fastPSF.php), reproduce
the same outputs with the C++ example app. Replicate the identical
inputs in the C++ file at `examples/generate-psf.cpp`. Write the
instructions in Raadme.

README.md

@@ -53,6 +53,36 @@ ninja all
 sudo ninja install
 ```
 
+## Running the examples
+
+First, follow the *Quick start* instructions to build the example app. Then, given the following microscope configurations in the screenshot...
+<img src="https://www.ee.cuhk.edu.hk/~tblu/monsite/demos/fastPSF/gui.png"/>
+
+... program the example C++ file at (https://github.com/MicroscPSF/MicroscPSF-Cpp/blob/main/examples/generate-psf.cpp)[examples/generate-psf.cpp]
+
+```c++
+microscope_params_t params{};
+params.NA = 1.4;
+params.ti0 = 150.0_um;
+params.ni = 1.5;
+params.ni0 = 1.5;
+params.pz = 2.0_um;
+
+precision_li2017_t precision{};
+precision.num_basis = 153;
+precision.rho_samples = 1000;
+
+const auto psf =
+    makePSF(params, {0.1_um, 0.25_um}, {256, 128}, 0.610_um, precision);
+```
+
+Next, repeat the *Quick start* steps to re-compile the C++ app. Run `ninja test`
+to invoke the compiled example. Locate the outputs `psf_xy.pgm`, `psf_xz.pgm`,
+and `psf.h5`. The XZ cross-section of the C++-simulated PSF should match the
+screenshot above.
+
+<img src="examples/psf_xz.png"/>
+
 ## Appendix: Bessel function support
 
 - The original ISO C++ proposal: https://wg21.link/p0226r1

examples/generate-psf.cpp

@@ -10,9 +10,20 @@ int main() {
     namespace hdf5_opts = arma::hdf5_opts;
     using namespace ::units::literals;
 
+    microscope_params_t params{};
+    params.NA = 1.4;
+    params.ti0 = 150.0_um;
+    params.ni = 1.5;
+    params.ni0 = 1.5;
+    params.pz = 2.0_um;
+
+    precision_li2017_t precision{};
+    precision.num_basis = 153;
+    precision.rho_samples = 1000;
+
     const auto psf =
-        makePSF(microscope_params_t{}, {0.1_um, 0.25_um}, {120, 63}, 0.530_um, precision_li2017_t{});
-#ifdef ARMA_USE_HDF5
+        makePSF(params, {0.1_um, 0.25_um}, {256, 128}, 0.610_um, precision);
+#ifdef  ARMA_USE_HDF5
     std::cout << "Saving volume to HDF5...\n";
     psf.save(hdf5_name("psf.h5", "psf", hdf5_opts::trans));
     std::cout << R"(Done.