outsig=rampdown(siglen);
rampdown(siglen) will return a falling ramp function of length siglen. The ramp is a sinusoid starting from one and ending at zero. The ramp is centered such that the first element is always one and the last element is not quite zero, such that the ramp fits with following zeros.
rampdown(L,wintype) will use another window for ramping. This may be any of the window types from firwin. Please see the help on firwin for more information. The default is to use a piece of the Hann window.