Unexpected Matlab Expression ?

I am new to coding and am unsure why my code does not work it says "Unexpected MATLAB expression" for the 3 in my code.

This is my code E(x)= [-1 1] 3 . * exp (1) . ^ ((-x)./4)

Any help is appreciated

[Jose Marques]

Should be something between [-1 1] and 3.* ? What this represents?

[Jose Marques]

Maybe it is better to explain what the expression means.

[Natalie Brehaut]

it is supposed to be an envelope to another function, I have tried to add .* in between but that comes up as unexpected MATLAB Operator

[Natalie Brehaut]

I am supposed to code the function E(x)= plus or minus 3e^(-x/4)

Answer 1

[Jose Marques]

Natalie, try this:

E= [-1 1] * 3 *( exp (1) .^ ((-x)/4))

E will be a matrix 1x2 that first element is positive value and second will be the negative value

[Natalie Brehaut]

When that is put in it says that the Matrix dimensions must agree

[Jose Marques]

Are you using the matrix E after that? Post you intire code; thus, we can be helpfull

[Natalie Brehaut]

Trial>> x= 1: 0.1 : 10; Trial>> y= 3 . * exp (1) .^ ((-x)/4) . * sin (2 . * x) y= 3 . * exp (1) .^ ((-x)/4) . * sin (2 . * x) ↑ Error: Unexpected MATLAB operator.

Trial>> E= [-1 1] * 3 *( exp (1) .^ ((-x)/4)) Error using * Inner matrix dimensions must agree.

I am just very lost in what is wrong with my codes

[Jose Marques]

A tip: you must use .* to element wise multiplication: https://www.mathworks.com/help/matlab/ref/times.html

[Jose Marques]

Natalie, have you ever use the for loop? Do you just wanna two values for E?

x=1:0.1:10;
for i=1:size(x,2)
    y(i) = 3 * exp (1) .^ ((-x(i))/4) * sin (2 * x(i));   
    E= [-1 1] * 3 *( exp (1) .^ ((-x(i))/4));
end
plot(y)

[Natalie Brehaut]

THAT WORKED THANK YOU SO MUCH

[Jose Marques]

Nice work!