Program sftrapez | Convolution with a trapezoidal filter. 
[SYNOPSIS]
sftrapez < in.rsf > out.rsf frequency=
[PARAMETERS]
floats  | frequency | = |   | 	frequencies (in Hz), default: (0.1,0.15,0.45,0.5)*Nyquist  [4]
[DIRECTORY]
system/generic
