Incorrect use of '=' operator. To assign a value to a variable, use '='. To compare values for equality, use '=='.

Question

Darwin Tuazon 2019-5-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/463848-incorrect-use-of-operator-to-assign-a-value-to-a-variable-use-to-compare-values-for-equal

评论： Dam 2022-12-9

Asking for help.

ERROR "Incorrect use of '=' operator. To assign a value to a variable, use '='. To compare values for equality, use '=='."

I already followed instruction above but another happened

ERROR 2: Illegal use of reserved keyword "for".

This is my code.

clc;
clear;
%dx/dt=ax-bxy Predator
%dy/dt=-cy+dxy prey
%constants as stated on the problem
a = 1.2;
b = 0.6;
c = 0.8;
d = 0.3;
%Defining the functions
%z[x,y]<=z(1,:)= y      z(2,:)=x
f=@(t,z)[ ...
    +a*z(2)-b*z(2)*z(1) 
    -c*z(1)+d*z(2)*z(1)
fx==@(t,x,y) a*x - b*x*y;
fy==@(t,x,y) -c*y + d*x*y;
%Initial Conditions
t(1)=0; %time
% x(1)=2; %predator
% y(1)=1; %prey
z(:,1)=[1,2];
%step size
h = 0.001;
tfinal = 30;
N = 1000;
%Loop
for i=1:N
    Update time
    t(i+1)=t(i)+h;
    %update for z
    k1=f(t(i),     z(:,i));
    k2=f(t(i)+h/2, z(:,i)+h/2*k1);
    k3=f(t(i)+h/2, z(:,i)+h/2*k2);
    k4=f(t(i)+h,   z(:,i)+h    *k3);
    z(:,i+1)=y(:,i) +h/6*(k1+ 2*k2 +2*k3 +k4);
end
%plotting
figure(1)
clf(1)
plot(t,y(1,:))
hold on
plot(t,y(2,:))
xlabel('Time')
ylabel('Populations')
hold off

Thank you and have a nice day

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Answer 1

Stephen23 2019-5-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/463848-incorrect-use-of-operator-to-assign-a-value-to-a-variable-use-to-compare-values-for-equal#answer_376484

编辑：Stephen23 2019-5-24

在 MATLAB Online 中打开

The actual problem starts on this line:

f=@(t,z)[ ...

because your code is missing the matching ]

Using = was correct.

Note that you should use colon or linspace to generate t, rather than the inefficient method that you use now.

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Darwin Tuazon 2019-5-24

Thank you so much for your response.

How can I revised my code?

Stephen23 2019-5-24

"How can I revised my code?"

Add the ] at the end of the concatenation.

Change back to =

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Answer 2

Tareq Rahmani 2020-3-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/463848-incorrect-use-of-operator-to-assign-a-value-to-a-variable-use-to-compare-values-for-equal#answer_421481

what is wrong here :

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Stephen23 2020-3-23

@Tareq Rahmani: in MATLAB square brackets are a concatenation operator. What are you concatenating?

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Answer 3

Simbarashe Zuva 2021-12-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/463848-incorrect-use-of-operator-to-assign-a-value-to-a-variable-use-to-compare-values-for-equal#answer_861215

编辑：Walter Roberson 2021-12-24

在 MATLAB Online 中打开

I also have the same problem with my code

The problem on line 40

I do i go about this error? I'm really new to matlab

% Dhtr and Dhte, for HOG of the input samples
u = ones(1,1600);
ytr = [u 2*u 3*u 4*u 5*u 6*u 7*u 8*u 9*u 10*u];
H = [];
 
for i = 1:1600
    xi = X1600(:,i);
    mi = reshape(xi,28,28);
    hi = hog20(mi,7,9);
    H = [H hi];
end
Dhtr = [H; ytr];
Hte = [];
for i = 1:length(Lte28)
    xi = Te28(:,i);
    mi = reshape(xi,28,28);
    hi = hog20(mi,7,9);
    Hte = [Hte hi];
end
Dhte = [Hte; 1+Lte28(:)'];
% MATLAB code for constructing Dtr and Dte for the original training and test
data sets
u = ones(1,1600);
ytr = [u 2*u 3*u 4*u 5*u 6*u 7*u 8*u 9*u 10*u];
Dtr = [X1600; ytr];
Dte = [Te28; 1+Lte28(:)'];
[ori_ws,ori_f]= SRMCC_bfgsoriML(Dtr,'f_SRMCC','g_SRMCC',0.002,10,62);
Dte(785,:) = ones(1,10000);
[~,ori_ind_pre] = max((Dte'*ori_ws)');
K = 10;
ytest = 1+Lte28(:)';
ori_C = zeros(K,K);
for j = 1:K
    ind_j = find(ytest==j);
    for i = 1:K
        ind-pre_i = find(ori_ind_pre == i);
Incorrect use of '=' operator. Assign a value to a variable using '=' and compare values for equality using '=='.
        ori_C(i,j) = length(intersect(ind_j,ind_pre_i));
    end
end
[hog_ws,hog_f]= SRMCC_bfgsML(Dtr,'f_SRMCC','g_SRMCC',0.001,10,57);
Dte(785,:) = ones(1,10000);
[~,hog_ind_pre] = max((Dte'*hog_ws)');
K = 10;
ytest = 1+Lte28(:)';
hog_C = zeros(K,K);
for j = 1:K
    ind_j = find(ytest==j);
    for i = 1:K
        ind-pre_i = find(hog_ind_pre == i);
        hog_C(i,j) = length(intersect(ind_j,ind_pre_i));
    end
end