Sketch the analytical solution, using the formula below. HELP

clc

clear all

m=1

k=100

x0=5e-2

v0=30e-2

w=sqrt(k/m)

f=w/(2*pi)

t=1/f

n=10

x(1)=x0*cos(w*t)+(v0/w)*sin(w*t)

for n=2:n

x(n+1)=x(n-1)*cos(w*t(n-1))+(v0/w)*sin(w*t(n-1))

end

plot(t,x)

I am getting the error mesage "Index exceeds the number of array elements (1)." What am I doing wrong, please help

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Answer 1

[John D'Errico]

I might guess that you actually meant to MULTIPLY t with the value (n-1) in this exprssion:

x(n+1)=x(n-1)*cos(w*t(n-1))+(v0/w)*sin(w*t(n-1))

Instead, remember that MATLAB does not have implicit multiplication. You need to use the * or the .* operator as appropriate. Here, it will not matter which you use.

x(n+1)=x(n-1)*cos(w*t*(n-1))+(v0/w)*sin(w*t*(n-1))

As well, I would suggest that this next line of code is an incredibly bad idea:

for n=2:n

MATLAB does not charge you more, if you use a different variable name. MATLAB will not be more efficient. Reusing the same variable name there is going to cause you innumerable headaches.

What else? I think you have a problem in your code, because you NEVER actually define x(2). You defined x(1). Then your loop starts at n==2. Therefore the first time through the loop, you define x(n+1), where n = 2. So you defined x(3) as the next element. x(2) was never defined. However, you will use x(2) later on.

I predict this code will produce arbitrarily useless strangeness. But that is just a guess. And since we were never told what the actual forumula you want to produce, we are merely guessing.

Answer 2

[Image Analyst]

t is a scalar with value 0.6283. There is no second or third element of t so you can't index t with (n-1).