invalid expression. when calling a function or indexing a variable use parentheses.

Question

Gideon Gaiters 2022-4-25

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1704850-invalid-expression-when-calling-a-function-or-indexing-a-variable-use-parentheses

回答： Aditya 2023-11-23

T= (0.5) *(4) * (;, Y, (3))

function [t,Y] = dynamicsProjectMurphy()

%This is a simple example of solving ode's in matlab. You'll mostly need

%to focus on defining F within the odefun currently between lines 10 and

%16.

%1D Y = [x,v]

%2D Y = [x,y,vx,vy]

%3D Y = [x,y,z,vx,vy,vz]

function dYdt = odefun(~,Y)

m1 = 4;

m2= 2;

k1 = 20;

k2= 20;

g= 9.81;

F1 = -k1*Y(1)+k2*(Y(2)-Y(1))-m1 * g;

F2 = k2 * (Y(1)-Y(2))-m2 *g;

a1 = F1/m1;

a2 = F2/m2;

dYdt = [Y(3);Y(4); a1; a2]; %dYdt = [v;a]

end

tspan = [0 10];%solve ode from t=0 to t=10

y0 = [1,1,0,0]; %start at x = 0.5 and v = 0

[t,Y] = ode45(@odefun,tspan,y0); %solve ode

figure(1)

plot(t,Y)

legend('x','v')

xlabel('t')

end

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DGM 2022-4-26

在 MATLAB Online 中打开

T= (0.5) *(4) * (;, Y, (3))

Yes, that's an invalid expression. I can't begin to guess what it's intended to mean. Not only is it invalid, I don't see where it's being used anywhere in the code and I don't see where it's getting Y either.

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Answer 1

Aditya 2023-11-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1704850-invalid-expression-when-calling-a-function-or-indexing-a-variable-use-parentheses#answer_1358547

在 MATLAB Online 中打开

Hello Gideon,

It appears that you've encountered an "invalid expression" error in your code. The issue is due to the following line:

T = (0.5) * (4) * (;, Y, (3))

This line contains syntax errors. In MATLAB, when calling a function or indexing an array, you need to use parentheses appropriately. To correct this issue, you should update your code like this:

% Ensure Y is initialized with your data before this line 
T = 2 * Y(:, 3); 

Please make sure that the matrix `Y` is defined and contains at least three columns before this line is executed. If this line in question is not related to the rest of your function and is not needed, you may simply remove it.

Hope this helps!