Spectral Analysis Example

Purpose

The purpose of the example is to show you the following:

• How to use the MATLAB Builder NE product to create a component (SpectraComp) containing more than one class

• How to access the component in a C# application (SpectraApp.cs), including use of the MWArray class hierarchy to represent data

  Note   For complete reference information about the MWArray class hierarchy, see the MWArray Class Library Reference (available online only).

• How to build and run the application, using the Visual Studio .NET development environment

The component SpectraComp analyzes a signal and graphs the result. The class, SignalAnalyzer, performs a fast Fourier transform (FFT) on an input data array. A method of this class, computefft, returns the results of that FFT as two output arrays—an array of frequency points and the power spectral density. The second class, Plotter, graphs the returned data using the plotfft method. These two methods, computefft and plotfft, encapsulate MATLAB functions.

The computefft method computes the FFT and power spectral density of the input data and computes a vector of frequency points based on the length of the data entered and the sampling interval. The plotfft method plots the FFT data and the power spectral density in a MATLAB figure window. The MATLAB code for these two methods resides in two M-files, computefft.m and plotfft.m, which can be found in:

matlabroot\toolbox\dotnetbuilder\Examples\VS8\NET\SpectraExample\SpectraComp

 computefft.m

function [fftData, freq, powerSpect] = ComputeFFT(data, interval)
%COMPUTEFFT Computes the FFT and power spectral density.
%   [FFTDATA, FREQ, POWERSPECT] = COMPUTEFFT(DATA, INTERVAL)
%   Computes the FFT and power spectral density of the input data.
%   This file is used as an example for the .NET Builder
%   Language product.
%   Copyright 2001-2003 The MathWorks, Inc.
if (isempty(data))
   fftdata = [];
   freq = [];
   powerspect = [];
   return;
end
if (interval <= 0)
   error('Sampling interval must be greater then zero');
   return;
end
fftData = fft(data);
freq = (0:length(fftData)-1)/(length(fftData)*interval);
powerSpect = abs(fftData)/(sqrt(length(fftData)));

 plotfft.m

function PlotFFT(fftData, freq, powerSpect)
%PLOTFFT Computes and plots the FFT and power spectral density.
%   [FFTDATA, FREQ, POWERSPECT] = PLOTFFT(DATA, INTERVAL)
%   Computes the FFT and power spectral density of the input data.
%   This file is used as an example for the .NET Builder
%   Language product.
%   Copyright 2001-2003 The MathWorks, Inc.
len = length(fftData);
    if (len <= 0)
        return;
    end
    plot(freq(1:floor(len/2)), powerSpect(1:floor(len/2)))
    xlabel('Frequency (Hz)'), grid on
    title('Power spectral density')

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Procedure

1. If you have not already done so, copy the files for this example as follows:

   1. Copy the following folder that ships with the MATLAB product to your work folder:

      matlabroot\toolbox\dotnetbuilder\Examples\VS8\NET\SpectraExample
      

   2. At the MATLAB command prompt, cd to the new SpectraExample subfolder in your work folder.

2. Write the M-code that you want to access.

   This example uses computefft.m and plotfft.m, which are already in your work folder in SpectraExample\SpectraComp.

3. While in MATLAB, issue the following command to open the Deployment Tool window:

   deploytool

4. Build the .NET component. See the instructions in Building Your Component for more details. Use the following information:

   Project Name	SpectraComp
   Class Names	PlotterSignalAnalyzer
   Files to compile	computefft.mplotfft.m

5. Write source code for an application that accesses the component.

   The sample application for this example is in SpectraExample\SpectraCSApp\SpectraApp.cs.

   The program listing is shown here.

    SpectraApp.cs

   // *******************************************************************************
   //
   //SpectraApp.cs
   //
   // This example demonstrates how to use MATLAB Builder NE to build a component
   // with multiple classes.
   //
   // Copyright 2001-2008 The MathWorks, Inc.
   //
   // *******************************************************************************
   
   using System;
   
   using MathWorks.MATLAB.NET.Utility;
   using MathWorks.MATLAB.NET.Arrays;
   
   using SpectraComp;
   
   namespace MathWorks.Examples.SpectraApp
   {
     /// <summary>
     /// This application computes and plots the power spectral density of an input signal. 
     /// </summary>
     class SpectraCSApp
       {
         #region MAIN
   
         /// <summary>
         /// The main entry point for the application.
         /// </summary>
         [STAThread]
         static void Main(string[] args)
           {
             try
               {
                 const double interval= 0.01;  // The sampling interval
                 const int numSamples= 1001;   // The number of samples
   
                 // Construct input data as sin(2*PI*15*t) + (sin(2*PI*40*t) plus a
                 // random signal.  Duration= 10; Sampling interval= 0.01
                 MWNumericArray data= new MWNumericArray(MWArrayComplexity.Real, MWNumericType.Double, numSamples);
   
                 Random random= new Random();
   
                 // Initialize data 
                 for (int idx= 1; idx <= numSamples; idx++)
                   {
                     double t= (idx-1)* interval;
   
                     data[idx]= Math.Sin(2.0*Math.PI*15.0*t) + Math.Sin(2.0*Math.PI*40.0*t) + random.NextDouble();
                   }
   
                 // Create a new signal analyzer object
                 SignalAnalyzer signalAnalyzer= new SignalAnalyzer();
   
                 // Compute the fft and power spectral density for the data array
                 MWArray[] argsOut= signalAnalyzer.computefft(3, data, interval);
   
                 // Print the first twenty elements of each result array
                 int numElements= 20;
   			        
                 MWNumericArray resultArray= new MWNumericArray(MWArrayComplexity.Complex, MWNumericType.Double, numElements);
   
   			        for (int idx= 1; idx <= numElements; idx++)
   			          {
   				          resultArray[idx]= ((MWNumericArray)argsOut[0])[idx];
   			          }
   
   			        Console.WriteLine("FFT:\n{0}\n", resultArray);
   
                 for (int idx= 1; idx <= numElements; idx++)
                   {
                     resultArray[idx]= ((MWNumericArray)argsOut[1])[idx];
                   }
   
                 Console.WriteLine("Frequency:\n{0}\n", resultArray);
   
                 for (int idx= 1; idx <= numElements; idx++)
                   {
                     resultArray[idx]= ((MWNumericArray)argsOut[2])[idx];
                   }
   
                 Console.WriteLine("Power Spectral Density:\n{0}", resultArray);
   
                 // Create a new plotter object
                 Plotter plotter= new Plotter();
   
                 // Plot the fft and power spectral density for the data array
                 plotter.plotfft(argsOut[0], argsOut[1], argsOut[2]);
   
                 Console.ReadLine();  // Wait for user to exit application
               }
   
             catch(Exception exception)
               {
                 Console.WriteLine("Error: {0}", exception);
               }
             }
   
           #endregion
       }
   }
   

   The program does the following:

   • Constructs an input array with values representing a random signal with two sinusoids at 15 and 40 Hz embedded inside of it

   • Creates an MWNumericArray array that contains the data

   • Instantiates a SignalAnalyzer object

   • Calls the computefft method, which computes the FFT, frequency, and the spectral density

   • Instantiates a Plotter object

   • Calls the plotfft method, which plots the data

   • Uses a try/catch block to handle exceptions

   The following statement

   MWNumericArray data= new MWNumericArray(MWArrayComplexity.Real, 
   MWNumericType.Double, numSamples);

   shows how to use the MWArray class library to construct a MWNumericArray that is used as method input to the computefft function.

   The following statement

   SignalAnalyzer signalAnalyzer = new SignalAnalyzer(); 

   creates an instance of the class SignalAnalyzer, and the following statement

   MWArray[] argsOut= signalAnalyzer.computefft(3, data, interval);
   

   calls the method computefft.

6. Build the SpectraApp application using Visual Studio .NET.

   1. The SpectraCSApp folder contains a Visual Studio .NET project file for this example. Open the project in Visual Studio .NET by double-clicking SpectraCSApp.csproj in Windows Explorer. You can also open it from the MATLAB desktop by right-clicking SpectraCSApp.csproj > Open Outside MATLAB.

   2. Add a reference to the MWArray component, which is matlabroot\toolbox\dotnetbuilder\bin\architecture\framework_version
      \mwarray.dll.

   3. If necessary, add (or fix the location of) a reference to the SpectraComp component which you built in a previous step. (The component, SpectraComp.dll, is in the \SpectraExample\SpectraComp\x86\V2.0\Debug\distrib subfolder of your work area.)

7. Build and run the application in Visual Studio .NET.

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