Expression (equation)

Hello, how to define an expression, for example 1-e^(-At) where I can define and change parameters A and t and than figure changes of the curve in a graph.

Thanks

Answer 1

[Paulo Silva]

Simplest version I can think of

t=0:0.1:100;             % Time vector
A=0.1;                   % Value of A that you can change
plot(t,1-exp(-A(n)*t))   % Represent it on a figure

If you place the cursor on the value of A you can try several values using the Editor tools (look on the tools of your editor window - 1.0 + ... press those symbols and the script runs with a new value for A)

Just for fun here's a version using subplots

clf
t=0:0.1:10;
A=[0.01 0.1 0 1];
for n=1:4
subplot(2,2,n)
plot(t,1-exp(-A(n)*t))
title(['A=' num2str(A(n))])
end

[Jan]

Thanks for answer, but when I've tried it I got an error message in this: plot(t,1-exp(-A(n)*t)) % Represent it on a figure

[Jan]

Thanks the subplots are working. Could you give me more explanation what means n in the line: plot(t,1-exp(-A(n)*t))

[Sean de Wolski]

It's the loop iterator that changes the value of A in each subplot in the bottom example. I it's a copy/paste error in the top (example)

[Jan]

Is it possible to model it in the Simulink?

[Paulo Silva]

Yes it is possible and simple, just play with the blocks, t is a Ramp and A is a Constant Source

[Paulo Silva]

It took me about 2 minutes to do it, here's a few tips:

1- Start from the parenthesis expression A*t

2- To turn something negative just use a Gain block with value -1

3- Use the Math Function block for the exponential

[Jan]

How could I use 2 kinds of source for one output if I use Ramp for t and Constant for A? I used Mux for signals, but in the output are two curves.

Sorry about that but could you make a list of blocks which to use.

Thanks again

[Paulo Silva]

It's just basic math, you use the Product block with inputs A and t and connect that block output to the Math Function block

[Jan]

thx :)

Answer 2

[Sean de Wolski]

And to add on to Paulo's example:

t=0:0.1:100;    % Time vector
A=0.1; 
y = 1-exp(-A*t);  % Value of A that you can change
H = figure;
plot(t,y)
linkdata(H,'on');
shg;
pause(2) %watch the magic in 2 seconds
A = .8;
y = 1-exp(-A*t);

if you want it to automagically update when you change A or y.

[Paulo Silva]

nice one :)

[Jan]

Thanks a lot Sean :)

[Jan]

Is it possible to model it in the Simulink?