Changes to lfm demo --- make the sample rate constant and force a maximum no of samples.
Changes to lfm demo --- make the sample rate constant and force a maximum no of samples.

SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat