Use trapezoidal method to find the deflection at each measurement point.

Hi,

I have the following 21x2 matrix

I need to use loops and trapezoidal method to find the deflection at each measurement point. By using the trapz command I can find the overall result but I need guidance with how to find the deflection at each measurement point.

[Sean Flanagan]

cumtrapz gives me each answer for [f(x0)...f(x20]. Is there a way to write the code to give [f(x0)+f(x1)] = ans, [f(x0)+f(x1)+f(x2)] = ans, [f(x0)+f(x1)+f(x2)+f(x3)] = ans .....[f(x0)+f(x1)....+f(x19)+f(x20)] = ans, using for loops?

Answer 1

[James Tursa]

Sounds like you want the cumtrapz( ) function. If the assignment requires you to use loops, just code up the formula found in the trapz( ) doc:

https://www.mathworks.com/help/matlab/ref/trapz.html

[Sean Flanagan]

Thanks James

[Sean Flanagan]

cumtrapz gives me each answer for [f(x0)...f(x20]. Is there a way to write the code to give [f(x0)+f(x1)] = ans, [f(x0)+f(x1)+f(x2)] = ans, [f(x0)+f(x1)+f(x2)+f(x3)] = ans .....[f(x0)+f(x1)....+f(x19)+f(x20)] = ans, using for loops?

[Torsten]

Why

[f(x0)+f(x1)] = ans,

[f(x0)+f(x1)+f(x2)] = ans,

[f(x0)+f(x1)+f(x2)+f(x3)] = ans

.....

[f(x0)+f(x1)....+f(x19)+f(x20)] = ans ?

Don't you need

[f(x0)+f(x1)]/2 * (x1-x0) = ans

[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) = ans,

[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) + [f(x2)+f(x3)]/2 * (x3-x2) = ans

...

[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) + [f(x2)+f(x3)]/2 * (x3-x2) + ... + [f(x19) + f(x20)]/2 * (x20-x19) = ans

?

That's what cumtrapz does.

Otherwise, use cumsum(f) instead of cumtrapz(x,f).

[Sean Flanagan]

Thanks mate I must have done something wrong