# how to plot trapezoidal rule

조회 수: 74(최근 30일)
alp onur karacay 2021년 12월 29일
답변: Pratyush Roy 2022년 1월 7일
Hello i coded trapezoidal rule but how can i plot it ?here is my code
t = 0:0.2:2*pi;
f = @(x) 3*cos(t*1000);
a = 0;
b = 2*pi;
n = length(t)-1;
h =(b-a)/n;
for i=1:1:n-1
sum = sum + f(a+i*h);
end
result = h/2*(f(a)+f(b)+2*sum);
fprintf('%f',result);
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Torsten 2021년 12월 29일
Your variable "result" is just a single number, namely the approximated area under the function f in the interval [0:2*pi].
So what do you want to plot ? How the area develops from 0 to 2*pi ?

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### 채택된 답변

Pratyush Roy 2022년 1월 7일
Hi,
One can use the polyshape function to create polygons (trapezium in this case) and use hold on and off to show them in a single figure. The following code might be helpful to understand how this works:
h = 0.2;
t = 0:h:2*pi;
f = @(x) 3*cos(x*1000);
a = 0;
b = 2*pi;
n = length(t);
sum1 = 0;
plot(t,f(t));
hold on;
for i=0:1:n-1
sum1 = sum1 + f(a+i*h);
if (i>=0)
plot(polyshape([a+i*h,a+i*h,a+(i+1)*h,a+(i+1)*h],[0,f(a+i*h),f(a+(i+1)*h),0]),'FaceColor','red');
hold on;
end
end
hold off;
result = h/2*(f(a)+f(b)+2*sum1);
Hope this helps!

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