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Resample a Matrix by Ratio of Intergers
Syntax y = resample(x, Nup, Ndown)
Include: include spt\resample.oms
See Also expand , interpfft

ARGUMENTS:
   INPUTS:  
      x     = MATRIX, any numerical type.
      Nup   = SCALAR, any numerical type, interpolation factor.
              Input data is interpolated to Nup times as many
              input samples. Coerced to INTEGER before internal
              processing.
      Ndown = SCALAR, any numerical type, decimation factor.
              Every Ndown-th sample of the interpolated data is
              returned. Coerced to INTEGER before internal
              processing.
   RETURN: MATRIX, Column-wise resampled version of input.

Description

Resample input data x by interpolating UP to Nup times the input number of samples, then, decimating down by a factor of Ndown.

Each column of an input matrix 'x' is resampled by first interpolating up by factor Nup, then decimating down by factor Ndown. Interpolation is done by the SPT function 'interpfft()' which uses a fourier transform method that assumes the data is cyclic. Decimation is done simply choosing every Ndown'th element of the interpolated column. This function simulates resampling a signal to the rational sampling rate Nup/Ndown. Output return length is a function of choice of Nup and Ndown.

Nup and Ndown are coerced to INTEGER before local processing. Nup and Ndown must each be >= 1 or 'novalue' is returned. If both are equal to 1 the original input is returned.

Data input may be of any numerical type. Return type is always type DOUBLE. Data input is coerced to DOUBLE before local processing. Row dimension of data input must be at least 2 except for the special case a row vector input which is treated as a column vector with a row vector return.

Example

# Interpolate a Squarewave
Nup   = 5
Ndown = 3
a     = fill( 1, Nin/4, 1)
b     = fill(-1, Nin/4, 1)
x     = { a, b, a, b }     # Test signal
y     = resample(x, Nup, Ndown)

 Plotting both input and output: