Write a script that prompts the user to input a function, f(x),

Question

libin danial 2012-8-2

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Write a script that prompts the user to input a function, f(x), and the limits of integration, a and b. The script should approximate the integral of the function from a to b, using the Trapezoid Rule. The script should also generate a plot of the function AND the piecewise-linear approximation to the function used in the Trapezoid Rule.

this is what i have soo far

clc,clear all, close all

f=str2func(['@(x)' input('Enter f(x):','s')]);
x=linspace(a,b,N);
N=input('define n=');
a=input('insert lower limit=');
b=input('insert upper limit=');
x=linspace(a,b,N);
h=(b-a)/(N-1);
for i=1:N-1;
T=T+h*(((f(x(i)))+(f(x(i+1))))/2);
end
plot(a,b)

am i doing something wrong

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Oleg Komarov 2012-8-2

编辑：Oleg Komarov 2012-8-2

在 MATLAB Online 中打开

You can aslo safely drop the too many ()

h*(f(x(i))+f(x(i+1)))/2

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Answer 1

Babak 2012-8-2

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在 MATLAB Online 中打开

In the first line of your code you cannot say

x=linspace(a,b,N);

because a, b and N are not yet defined there.

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Babak 2012-8-2

remove that line... you also need to use

for i=1:N-1

insetad of

for i=1:N-1;

I mean without semicolon.

In your statement:

T=T+h*(((f(x(i)))+(f(x(i+1))))/2);

T needs to be defined in Advance... you can sat T=0; at the beginning of your code for example.

Note: I recommend you using func() or fun() instead of f() because MATLAB has issues evaluating f(g(x)) when function names f, g are single characters.

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