how to create trapezoidal wave form as shown in fig in attached file?

i am using trapezoid function to create a trapezoidal wave form but i am not getting desired result.please help code is here;

function s = trapezoid(t)
%TREPEZOID Trapezoid wave generation.
%   TRAPEZOID(T) generates a square wave with period 2*Pi for the
%   elements of time vector T.  TRAPEZOID(T) is like SQUARE(T), only
%   it creates a square wave with peaks of +1 to -1 instead of
%   a sine wave.
%   
%   For example, generate a 30 Hz square wave:
%        t = 0:.0001:.0625;
%        y = square(2*pi*30*t);, plot(t,y)
%
%   I pretty much stole this from square, so see that.
%   See also SQUARE

%   Author(s): Jordan Firth, 2 Sep 2010
%   $Revision: 0.0 $  $Date: 2007/12/14 15:06:21 $

% compute values of t normalized to (pi/4,9*pi/4)
tmp = mod(t-pi/4,2*pi);

tmp = mod(t+pi/4,2*pi);

a = (tmp < pi/2);
b = (tmp >= pi/2 & tmp < pi);
c = (tmp >= pi & tmp < 3*pi/2);

rise = 2*tmp/pi;
fall = -2*(tmp-pi)/pi+1;

nodd = a.*rise + b + c.*fall;

s = 2*nodd-1;

and using this function i am trying to create waveform as i need.

%trapezoid wave form
t = -5:.001:5;
y1 = trapezoid((2*pi*0.5*t)-pi/2);
y2=trapezoid((2*pi*0.5*t)+0);
y3=trapezoid((2*pi*0.5*t)+pi/2);
plot(t,y1,t,y2,t,y3)

%