MATLAB: Subs Command

substitution

Is it possible to make an array in a function then substitute a certain element to another element. I have a beam equation with certain forces on different parts. So I created a variable for the length and am given an expression for the whole beam. So I split the equation into multiple parts and now want to evaluate each piece through different lengths. Any help would be appreciated. Thanks

Best Answer

From your description I gather that you want to swap out a range of values from an array into new indices within that array. You can modify values in a range by simply passing that range as a subscript on the left and passing new values (the same length) on the right...

Let's say I have the array:

x = 1:20

I can swap 5 elements from either end like this:

x([1:5 15:20]) = x([15:20 1:5])

Or duplicate sections

x(1:4) = x(5:8)

Or just mess it up

x([5 9 20 13:16]) = x([1 4 7 10 11 18 19 20])

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MATLAB: Graph figure wont show

If you're absolutely required to use a for loop, just add an index to y

% Clean up
close all;
clc;
clear all;
l=25;
E=200e9;
I=350e-6;
w=6e3;
x1=linspace(0,l/2,25)
for k = 1 : length(x1)
    y1(k)=(-(w*x1(k))/(384*E*I))*(16*(x1(k)^3)-24*l*(x1(k)^2)+9*(l^3))
end
  x2=linspace(l/2,l,26)
for k = 1 : length(x2)
    y2(k)=(-(w*x2(k))/(384*E*I))*(8*(x2(k)^3)-24*l*(x2(k)^2)+17*x2(k)*(l^2)-(l^3))
end
x = [x1, x2];
y = [y1, y2];
plot(x,y, 'bo-')
grid on;

MATLAB: Please i want to solve linear equations which takes the form of AX=B where x is the unknown variables but i have another unknown in row 2 of matrix B how i can not solve this problem

You have 6 equations in 7 unknowns. You do not have enough information to determine all of the variables x1, x2, x3, x4, x5, x6, and y .

syms y x1 x2 x3 x4 x5 x6
A=[2-j*3   -0.9+j*9   0        0       0    -1+j*19;
       -0.9+j*9   2-j*3   j*9       0       0   -1+j*9;
        0         j*9     17-j*3   -17+j*2  0     0;
        0         0       -17+j*2   17-j*4  j*2   0;
        0         0       0         j*2     -j*25 0;
        -1+j*19   -1+j*19 0         0        0    3-j*39;      ];
B=[5;y;0;0;2;0]; % y is the unknown variable
X=[x1;x2;x3;x4;x5;x6];
sol = solve(A*X == B, X)

This will have sol.x1 through sol.x6, all dependent on the variable y. If you knew any one x* value then you could calculate y. For example,

Y = solve(sol.x1 == 3+4*j, y)

Best Answer

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MATLAB: Graph figure wont show

MATLAB: Please i want to solve linear equations which takes the form of AX=B where x is the unknown variables but i have another unknown in row 2 of matrix B how i can not solve this problem

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