Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

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Navaneetha Krishnan Murugadoss
编辑： Torsten 2022-3-14
for Y(1) =1:1:numel(t)
↑
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

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回答（4 个）

Torsten
Torsten 2022-3-13
编辑：Torsten 2022-3-13
Y(1) is a scalar (single number), 1:numel(t) is a vector. You can't set a scalar to a vector.
Use an unused variable name instead, e.g.
for k = 1:numel(t)
Image Analyst
Image Analyst 2022-3-13
Try
for k = 1 : numel(t)
this_t = t(k);
Y(k) = 5 * this_t ^ 2 + 42; % Replace with whatever your formula for Y is.
end
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Jan
Jan 2022-3-13
编辑：Image Analyst 2022-3-13
Which error message do you get? Avoid overdoing the parentheses:
Fyt = @(t,Y) [-K * Y(1) * Y(2); ...
-Yb * K * Y(1) * Y(2); ...
Yp * K * Y(1) * Y(2)];
This looks cleaner.
Note that you have defined "Fyt", but call "fyt" later.
This cannot work also:
k2 = fyt ((Y(1)+0.5*h, Y(2)+0.5*h*k1));
% ^ ^
Here the inner parentheses combine the two arguments, but the function Fyt (not fyt) should get 2 arguments. Better:
k2 = Fyt(Y(1) + 0.5 * h, Y(2) + 0.5 * h * k1);

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Walter Roberson
Walter Roberson 2022-3-13
The variable for a for loop must be a plain unindexed variable.
Torsten
Torsten 2022-3-13
编辑：Torsten 2022-3-13
h=3600;
A0=1;
B0=3;
P0=0;
K=5*10^-5;
Yb=1;
Yp=0.15;
t = 0:0.1:10;
fyt = @(t,y) [(-K*y(1)*y(2));
(-Yb*(K*y(1)*y(2)));
(Yp*(K*y(1)*y(2)))];
Y = zeros(3,numel(t))
Y(1,1) = 1.0;
Y(2,1) = 3.0;
Y(3,1) = 0;
for i=1 : numel(t)-1
k1 = fyt(t(i),Y(:,i));
k2 = fyt(t(i)+0.5*h,Y(:,i)+0.5*h*k1);
k3 = fyt(t(i)+0.5*h,Y(:,i)+0.5*h*k2);
k4 = fyt(t(i)+h,Y(:,i)+h*k3);
Y(:,i+1) = Y(:,i) + (h/6)*(k1+2*k2+2*k3+k4);
end
figure (1)
plot(t,Y(1,:))
figure (2)
plot(t,Y(2,:))
figure (3)
plot(t,Y(3,:))
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