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.

TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat