I get error when I try to plot sigmoid function

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);

Answer 1

[Star Strider]

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.

.

Answer 2

[Sam Chak]

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
title('ReLU-like function')
xlabel('dt')

[cindyawati cindyawati]

Thank you for your response, M1(i) is parameter something that has depending by time (i) and has a sigmoid function.

[cindyawati cindyawati]

M1 (i) have the form empty array because M1(i) must repeated by time

[Sam Chak]

You're welcome, @cindyawati cindyawati. Thanks for your clarification.

Answer 3

[Walter Roberson]

dt=-30:h:30;

dt is a vector

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

t(i) is a scalar. Add the complete vector dt and you will get a vector. But you cannot store a vector in the scalar location t(i+1)

[Walter Roberson]

It is really strange to have time go backwards:

h=0.01;
dt=-30:h:30;
t = cumsum(dt);
plot(t)

I suspect you want t itself to be -30 to +30 -- that you want

t(1) = -30;
dt = h;
for i= 1:length(t)
    t(i+1)=t(i)+dt;
end
plot(t)

[cindyawati cindyawati]

Thank you for your answer. Anyway, how to store t(i)+dt to vector location?

[cindyawati cindyawati]

t mean for time

[Walter Roberson]

Like @Star Strider showed,

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