how to do a loop and call a function

function [g1]=func2(L,D,P,r,c,a,t)

g1=(((3*c)/(P*r))*((((D*(t-a))/L))-(L/6)));

end

function [g2]=func3(L,D,P,r,c,Y,t)

g2=1-((c/P)*exp(((-3*D)/(r*L))*(t-Y)));

end

hi guys. can someone help me? i have this to funtion and i have to set all the variable L,D,P,r,c,a and Y as a input and i have to do a for loop for t from 0 to 100 using this eqution and have to set the solution when a<t<=Y the it will use the first function and when t>Y it will use the second function and when t<a the fuction will be g=0 .but i don't know how to do it. so please help me

[Stephen23]

"...i have to do a for loop for t from 0 to 100 ..."

Is it really required to use a loop? If the other parameters are scalar, it would be trivial to vectorize those functions.

"...but i don't know how to do it"

Use logical indexing:

https://www.mathworks.com/help/matlab/math/array-indexing.html

[liyana nadirah]

sorry i don't get it. can you explain

Answer 1

[David Hill]

c=;
P=;
r=;
D=;
a=;
L=;
Y=;
t1=0:a;
t2=a+1:Y;
t3=Y+1:100;
g=[zeros(1,length(t1)),(((3*c)/(P*r))*((((D*(t1-a))/L))-(L/6))),1-((c/P)*exp(((-3*D)/(r*L))*(t3-Y)))];
t=0:100;

Answer 2

[Stephen23]

As described in the question, you will have to do something like this:

L = ???;
D = ???;
P = ???;
r = ???;
c = ???;
a = ???;
Y = ???;
t = 0:???:100;
%
N = numel(t);
g = zeros(1,N); % this already fulfills the t<a requirement.
for k = 1:N
    if t(k)>Y
        g(k) = func3(??????, Y, t(k));
    elseif t(k)>a
        g(k) = func2(??????, a, t(k));
    end
end

I left a few trivial things for you to complete (you need to replace all of the ???).

Both functions will need to be saved somewhere where they are visible to this code.

[liyana nadirah]

did i have to this in the new script?

[Stephen23]

"did i have to this in the new script?"

That depends entirely on where you saved those two functions, which you have not told us.

1. If you have saved both functions together in one Mfile then you can add my code within a third function inside the same Mfile (or for MATLAB versions >=R2016b by adding a script at the start of the Mfile).
2. If you saved each function in its own separate Mfile then you can add my code to any script or function.

[liyana nadirah]

then what if i want to plot g against time and i have to do it for various of L and have to combine all the graph in one figure

[Stephen23]

"then what if i want to plot g against time and i have to do it for various of L and have to combine all the graph in one figure"

Probably the simplest approach would be to add another loop, something like this:

L_vec = [... vector of L values...];
hold off
for kk = 1:numel(L_vec)
    L = L_vec(kk);
    ... the rest of the code
    plot(t,g)
    hold on
end

[liyana nadirah]

then what if i want to plot r from 0 to 1.42 and fix the t

[Stephen23]

"then what if i want to plot r from 0 to 1.42 and fix the t"

If you only want to vary the r value then do the same like I showed you for L.

If you want to vary multiple different values then use ndgrid to generate all permutations.