Matlab plotting of a trapezoidal cuve

Question

DEBASHIS PANDA 2015-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/259913-matlab-plotting-of-a-trapezoidal-cuve

回答： Satyajeet Sasmal 2015-12-15

Hello.. I want to plot a trapezoidal curve which is attached here. For that I have written following code but while plotting the value of pressure is not coming as a vector it is giving only a vector of only five value.I am not getting where is my fault plz help....

t(1)=0;
pl=.5;
ph=1.5;
f=2;
h=.1;
t1=0.45/f;
t2=t1+(.15/f);
t3=t2+(0.23/f);
t4=t3+(0.17/f);
%t=t1+t2+t3+t4
tau=1/f;
%p=zeros(1,101);
p(1)=0;
pavg=(ph+pl)/2;
pamp=(ph-pl)/2;
for m=1:1:10
  if (t(m)>= 0) && (t(m) <= t1)
      p(m+1)=pl+(((ph-pl)/t1)*t(m));
  elseif(t(m)>= t1) && (t(m) <= t2)
      p(m+1)=ph;
  elseif(t(m)>= t2) && (t(m) <= t3)
      p(m+1)=ph+(((pl-ph)/(t3-t2))*(t(m)-t2));
  elseif(t(m)>= t3) && (t(m) <= t4)
       p(m+1)=pl;
  end
    t(m+1)=t(m)+1;
end  end

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Answer 1

Satyajeet Sasmal 2015-12-15

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https://ww2.mathworks.cn/matlabcentral/answers/259913-matlab-plotting-of-a-trapezoidal-cuve#answer_203365

Hi Debashish,

I assume that you want to plot (p,t). But p just has 2 elements and that is why it does not allow it to be plotted against "t". You only get 2 values for p because the control inside the for-loop does not execute some of the if-elseif conditions. In fact, it only enters the if-elseif condition block on only 2 occasions and so you get only 2 values for p. Try giving an else condition to the if-elseif block and assign some value to p in such cases. Once "p" and "t" are the same length, you should be able to plot them.

-Satya