Numerical solution of symbolic equation

Could someone help me with my solving problems?

Here is my code. I would like to have numerical answers

clear;clc;

E = 2*10^11;
I = 4*10^-4;
F = 10000;
l = 2;

syms x

Mx = @(x) (F.*x);

phix = @(x) int(Mx,0,l);

fx = @(x) int(phix,0,l);

%x = 0:x_step:l;
x_step = 0.01;
x = 0:x_step:l;


M = solve(Mx,x) ;

[John D'Errico]

Numerical answers to what? It is not clear from your code as to what you imagine solve does, or what you want it to do.

Mx represents a straight line, a linear function of x, with slope F.

x is a vector of values for x, going from 0 to 2, using an increment of 0.01.

So what do you think solve does?

[Jesse]

M(x) = F * x

x min = 0;

x max = 2

I would likt to have the solved the integral of F*x with numerical solution.

[Walter Roberson]

phix = @(x) int(Mx,0,l);

You are ignoring the input x and integrating Mx over 0 to l (lower-case L)

fx = @(x) int(phix,0,l);

then you take the result, ignore the input x, and integrate phix over to to l (lower-case L)

I would likt to have the solved the integral of F*x with numerical solution.

Do you mean that you have a model parameter with an unknown value, that for each different in 0:x_step:l you want to solve

??

Or are you simply wanting

syms t B
fx = int(F*t, 0, B)
subs(fx, B, x)

which is to say, to get

[Jesse]

I guess more like this

syms x B
fx = int(F*x, 0, B)
subs(fx, B, x)

[Jesse]

I see it's quite the same. Maybe you can explain me your code, what does the B mean?

[Walter Roberson]

B is upper bound.

I was careful to use t instead of x to avoid conflict with your numeric x. After your syms x then x is symbolic and not your numeric vector. What you subs() in needs to be the numeric vector and if you store that vector in x then you cannot int() with respect to x as you must integrate with respect to something symbolic.

For the simple F*x of course your integral is going to be F*x.^2/2

[Jesse]

That's right. 1/2 F * x^2 + C.

Okay, and how to fill in the integral with data, could you help me?

[Walter Roberson]

F = 10000;
l = 2;
x_step = 0.01;
x = 0:x_step:l;

syms t B
fx = int(F*t, 0, B)
result = subs(fx, B, x)

or

F = 10000;
l = 2;
x_step = 0.01;
x = 0:x_step:l;

result = F * x.^2/2;

[Jesse]

Okay, so it isn't possible to generate a formula with matlab, integrate it, and get results?

[Jesse]

I have this and think it works how i would like it

clear;clc;

F = 10000;
l = 2;
x_step = 0.01;
x = 0:x_step:l;
syms t B
fx = int(F*t, 0, B)
result = subs(fx, B, x)

plot(result,x)

[Walter Roberson]

F = 10000;
l = 2;
x_step = 0.01;
x = 0:x_step:l;
syms t B
Mx = F*t;              %generate the formula
fx = int(Mx, 0, B)     %integrate it
result = subs(fx, B, x);
plot(x, result);      %plot it