MATLAB: How to achieve downsampling using an MATLAB file S-function in Simulink 7.4 (R2009b)

simulink

I am trying to create a block that takes in an input of varying sizes (512, 1024, 2048, etc.) and after scaling and processing, downsamples the input to produce only an integer fraction of the number of inputs. I have all the processing code, but I can't make the port dimensioning work. How do I do it ?

Best Answer

For frame based inputs and outputs, the output port dimensions are dependent on the input port dimensions; therefore the outport dimensions must be set in SetInputPortDimensions callback function. The attached single-rate model "testMult.mdl" demonstrates this using the S-function in MATLAB file "MDownsample.m". The model takes in a signal of frame size 2048x1 and outputs a signal of frame size 8x1.

Related Solutions

MATLAB: Do I receive an “Error in port widths or dimensions” error when I set default input dimensions in Simulink when the input ports are initialized dynamically

In order to use several ports which inherit their dimensions from the input ports, you can use the SetInpPortDims method as follows
block.RegBlockMethod('SetInputPortDimensions',  @SetInpPortDims); 
function SetInpPortDims(Block, port, dims) 
   Block.InputPort(port).Dimensions = dims;

The attached example illustrates this.

MATLAB: Downsampling image

Hi, You can use dyaddown() from the Wavelet Toolbox.

    x = randn(8,8);
    % this gives you 1st row, 1st column, 3rd row, 3rd colum, etc
    y = dyaddown(x,'m',1);
    % now this gives you 2nd row, 2nd column, etc
    y = dyaddown(x,'m',0);

Or you can use downsample() from the Signal Processing Toolbox. This gives you one polyphase matrix.

     Y = downsample(x,2,0);
     Y = (downsample(Y',2,0))';

This gives you the other:

       Y1 = downsample(x,2,1);
       Y1 = (downsample(Y1',2,1))';

Hope that helps,

Wayne

Best Answer

Related Solutions

MATLAB: Do I receive an “Error in port widths or dimensions” error when I set default input dimensions in Simulink when the input ports are initialized dynamically

MATLAB: Downsampling image

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