Fun with Waves in Matlab – Wave Equation Modeling



Matlab is cool. Math is cool. Enough said.
Amazing how all this beauty is held inside such a seemingly simple formula, the wave equation.
{ \partial^2 u \over \partial t^2 } = c^2 \nabla^2 u
This is the basics of the setup. It is a rectangular pool that can simulate perturbations based on the above wave equation. The model implements finite differences for its solution on the 2D mesh. e.g. (f_x = (f_i – f_[i-1]) / da)

Details of Model

The inner oscillations are a result of model error. I wasn’t sure if this error was from the size of the impulse or the size of the mesh. The variables needed to be isolated. I doubled the size of the mesh points in each direction. To keep the impulse size the same, the input was now a 2×2 impulse instead of a 1×1. As seen, the inner oscillations have a higher frequency compared to before. This means the model error of inner oscillation frequency is dependent on the mesh size.
I wondered what happens in real life when something gets dropped into a big bowl of water. It turns out that there is one big oscillation followed by medium sized ripples. Running the simulation with a bigger impulse and a very fine mesh, I obtain similar results. As shown, you can see one big oscillation followed by medium-sized ripples.
In addition to the medium-sized ripples, you can still see little oscillations of high frequency. As shown previously, these depend on the step size.
In real life, there are a discrete number of water molecules to move up and down. There aren’t infinitely many points in the mesh.
Maybe these frequencies that depend on the step size show up in real life too. Or maybe not.

Boundary Value Manipulation

Any Dirichlet boundary conditions* can be imposed by reassigning the boundary to its fixed value after every iteration. I wanted to see what happened on the shape of a guitar. It is interesting how there is sort of a mirror of the source in the front of the guitar. There was only one impulse applied to this shape, even though it looks like there is a smaller impulse on the top of the guitar.

*A Dirichlet boundary condition is a fancy word for a boundary that doesn’t move, like a wall that has a jump rope tied to it – or a guitar bridge with guitar strings tied to it.

Fun Experiment DOUBLE SLIT!! xD

Applying more Dirichlet boundary values to form two slits for waves to come out. Look at that beautiful diffraction pattern!! (:

Until next time

A Guitarist’s Guide To Overcoming Obnoxious Password Requirements


Annoyed with site’s complexity requirements?

Are the passwords “password” and “qwe123” no longer cutting it? Are websites not accepting “CorrectHorseBatteryStaple” due to lack of complexity?!?

Here’s a technique I came up with that helps me create memorable passwords that still meet obnoxious complexity requirements.

Pick your favorite guitar scale, in this example I’ll use the pentatonic scale.


From here, I imagine the keyboard as a fretboard. I will also press shift when I want to play the upper three strings.

My password is now “farw42FSRQ$!”. I usually call this good, but on some sites where I don’t want to security risk of duplicating a password, I will add the first letter of the site name. So for, my password would be “cfarw42FSRQ$!”

You can continue to apply this technique to learning songs as well. All you have to do is visualize the keyboard as a guitar fretboard. Having my password set as the crux riff to the crazy train solo helped me build the muscle memory needed to play that quickly and accurately.

How to tie a C# .NET GUI to a callable C# .NET class library dll from Excel VBA: Guided Minimum Framework Example



A minimum working example of how to tie a C# .NET GUI to a callable C# .NET class library dll from Excel VBA or another C# application.


This is a follow up to the non GUI example posted earlier




  • 1 Summary:
  • 2 Framework Structure
    • 2.1 ExampleTargetApp (GUI Application)
      • 2.1.1 MainWindow.xaml.cs
      • 2.1.2 HelloWorldService.cs
    • 2.2 ServiceDefinition
      • 2.2.1 IHelloWorldService.cs
    • 2.3 CallingDll
      • 2.3.1 ServiceProxy.cs
      • 2.3.2 ICallTargetApp.cs
      • 2.3.3 CallTargetApp.cs
  • 3 Example access from VBA

Framework Structure

The goal is to connect the piping features of WCF named piping class with the GUI features of the MainWindow class. C# does not support multiple inheritance, but that is fine. We only need an interface and C# supports that of course. We can create an interface from the GUI that the DLL will utilize to allow changes to the GUI from another application.

The framework consists of three projects within visual studio: ExampleTargetApp, ServiceDefinition, and CallingDll.

  • ExampleTargetApp contains the information for the GUI and handles what happens when elements of the GUI interact with the user, presumably via mouse and keyboard but could also be via function piping. This project also contains a service to make use of the pipes interface.
  • ServiceDefinition contains an interface for the functions to go through WCF pipes.
  • CallingDll uses the service interface to access functionality contained and defined in the ExampleTargetApp project

ExampleTargetApp (GUI Application)


Contains the elements of the GUI such as Button1_Click() and SelectRadio1()


Contains the service class using the service interface



Contains the service interface definition



Set up the service to work using the service contract defined in the ServiceDefinition project


Interface for calling DLL


Functions for calling DLL through the proxy


Example access from VBA


Load the dll “CallingDll” by selecting browse then going to the project build directory: C:\dev\AutomationComExample\CallingDll\bin\x86\Debug\CallingDll.tlb

Excel VBA Code 
Sub SelectHello()
    Dim targetApp As Object
    Set targetApp = CreateObject("CallingDll.CallTargetApp")
End Sub
Sub SelectGoodbye()
    Dim targetApp As Object
    Set targetApp = CreateObject("CallingDll.CallTargetApp")
End Sub
Sub SelectButton()
    Dim targetApp As Object
    Set targetApp = CreateObject("CallingDll.CallTargetApp")
End Sub

How to call a C# .NET class library from Excel VBA: Guided Example


I have made a GUI in C#. Now I want to create an API to use in vba to ease automation and make use of the team’s existing vba code. This guide gives a basic example of how to do that. Examples I found online were overly complicated and/or not so useful. This short guide should get you started in calling your C# .NET functions from Excel VBA. If you plan on using a GUI, see the other guide as this approach will run into problems. Please let me know if you have trouble.


Update: As it turns out, this does not effortlessly lead into a COM accessible GUI as I originally suspected. This documentation below works great until you try to add in the actual GUI application. For the GUI application, see this guide: How to tie a C# .NET GUI to a callable C# .NET class library dll from Excel VBA: Guided Minimum Framework Example

After making different “HelloWorldGUI via VBA/C#” style minimal working solution examples, I picked Named Pipes for now because it was the easiest solution I found (outside of COM exposed DLL solution below for non-gui applications. .NET 3.5+ required

Possible solutions included:

  • Run the GUI from the VBA – No, I want a standalone GUI that can be attached to
  • Use AutoItX3.dll to literally click the buttons and type using virtual keyboard and mouse – No, doable but overly difficult and complicated
  • Use .NET’s UI automation to control UI elements found through Windows SDK inspect tool – Pretty good, but since we have the GUI source code, there should be a more direct solution\
  • Use UDP port on local machine to link programs
  • Communicate through set memory location on computer – too low level. Something should already exist that does this safely without problems
  • Use WCF (Windows Communication Foundation) Named Pipes to communicate between VBA/C# and WPF (Windows Presentation Foundation) – Looks the cleanest and easiest way

Step-By-Step Guided Example

  • Step-By-Step Guided Example
  • 1. Create C# Library Class
  • 2. Make Library Class Visible as COM Library
  • 3. Call Public Functions from Excel VBA
  • 4. Deployment
    • Unblock the DLL (Windows Security)
    • Registering the Assembly
    •  Related articles
  • References

1. Create C# Library Class

Put this code in a new C# file in a new Visual Studio project. It is bare bones with one simple function that will later be called from Excel vba.

I named the project and solution both ZZTEST_EXCEL_LIB for easy finding in the excel references list.

Sample Code Collapse source
        publicDouble DotNetMethod_SQR(Double input) //Return the square of the input
            returninput * input;

2. Make Library Class Visible as COM Library

In the project properties, change the output type to Class Library

In Assembly Information, check “make assembly COM-Visible”

In the project properties under the build tab, check “Register for COM interop”

3. Call Public Functions from Excel VBA

In Excel, enable the developer tab and launch visual basic (google this step if unclear)

From visual basic, select tools and then references. Select the desired library, in this case “ZZTEST_EXCEL_LIB”

Run the VBA code
Collapse source
    MsgBox test1.DotNetMethod_SQR(5) 'The function made in C# should return the square the input, 5*5 = 25



4. Deployment

This is great, but it will only work on your computer. You must follow these steps to register the DLL on another computer. TK I am looking into building an installer to do this

Everything in the C:\Program Files (x86)\Maxim\GUI_BRIDGE path must be placed in this exact path on the target computer.

Unblock the DLL (Windows Security)

Registering the Assembly

Start the command prompt as administrator

In the terminal window, run regasm with /codebase option on the dll.

“C:\Windows\Microsoft.NET\Framework\v4.0.30319\RegAsm.exe” /codebase “C:\Program Files (x86)\Maxim\GUI_BRIDGE2\gui_bridge2_project\gui_bridge2_project\bin\Debug\ZZ_GUI_BRIDGE2_PROJECT.dll”

Regasm will warn about RA0000 ~ please give your assembly a strong name and re-register it. Types registered successfully.

References – debugging deployment issue