I get error when I try to plot sigmoid function

Question

cindyawati cindyawati 2023-5-9

0
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https://ww2.mathworks.cn/matlabcentral/answers/1960364-i-get-error-when-i-try-to-plot-sigmoid-function

评论： Sam Chak 2023-5-10

I try to plot equation with sigmoid function, but i get error

M1(1)=0;
t(1)=0;
h=0.01;
dt=-30:h:30;
t=zeros(length(dt),1);
M1=zeros(length(dt),1);
for i= 1:length(t)
    t(i+1)=t(i)+dt;
    M1(i+1)=M1(i)+1./(1+exp(-dt)); 
end
Unable to perform assignment because the left and right sides have a different number of elements.
plot(t,M1);

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Answer 1

Star Strider 2023-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/1960364-i-get-error-when-i-try-to-plot-sigmoid-function#answer_1231934

在 MATLAB Online 中打开

Subscript ‘dt’. However the loop is not necessary and does not appear to plot the desired function —

M1(1)=0;

t(1)=0;

h=0.01;

dt=-30:h:30;

t=zeros(length(dt),1);

M1=zeros(length(dt),1);

for i= 1:length(t)

t(i+1)=t(i)+dt(i);

M1(i+1)=M1(i)+1./(1+exp(-dt(i)));

end

plot(t,M1);

Mv = 1./(1+exp(-dt));

figure

plot(dt,Mv)

The second plot may be what you want.

.

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Answer 2

Sam Chak 2023-5-9

2
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https://ww2.mathworks.cn/matlabcentral/answers/1960364-i-get-error-when-i-try-to-plot-sigmoid-function#answer_1231999

在 MATLAB Online 中打开

Hi @cindyawati cindyawati

A pure sigmoidal logistic function looks like this

x = linspace(-10, 10, 20001);

S = 1./(1 + exp(-x));

figure(1)

plot(x, S), grid on

title('Sigmoidal Logistic function')

xlabel('x')

But yours looks like the ReLU-like (rectified linear unit) activation function due to the Iterative addition of M1(i). Can you clarify the type of sigmoid function that you are looking for?

M1(1) = 0;

t(1) = 0;

h = 0.01;

dt = -30:h:30;

t = zeros(length(dt), 1);

M1 = zeros(length(dt), 1);

for i= 1:length(t)

t(i+1) = t(i) + dt(i);

M1(i+1) = M1(i) + 1./(1+exp(-dt(i)));

end

figure(2)

plot(dt, M1(2:end)), grid on