Help with for loop and if else statement

I am writing to code for the attached capture 1 image, and it is supposed to obtain the graph as shown in the capture 2 image.

I used for and if-else statement to write the code, however it is not working. If possible can anyone look into it? Thanks in advance.

y=0:1000;
for i=0:length(y)
    if y(i) <= 10
        Q1=1;
    elseif (y(i) > 10) && (y(i)<100)
        Q2=0.32*y-2.2;
    else y(i) > 100
        Q3 =300/sqrt(y);
    end  
    Q=(Q1+Q2+Q3)
end
semilogx(y,Q)

Answer 1

[Image Analyst]

You need to index L and Q:

L = linspace(0, 200, 2000);
Q = ones(1, length(L)); % Initialize to 1
for k = 2 : length(L)
    if L(k) <= 10
        Q(k) = 1;
    elseif (L(k) > 10) && (L(k)<= 100)
        Q(k)=0.32 * L(k) - 2.2;
    elseif L(k) > 100
        Q(k) =300/sqrt(L(k));
    end
    %     Q=(Q1+Q2+Q3)
end
loglog(L, Q, 'LineWidth', 3);
grid on;
xlabel('L', 'FontSize', 20)
ylabel('Q', 'FontSize', 20)

Of course you don't need a loop - you can do it vectorized if you want but it's your homework so I didn't try to modify it too much.

[Rachna Singh]

Thank you

Answer 2

[Mathieu NOE]

hello

here you are .

Q andy must be indexed in the loop (Q(k) , y(k))

only one Q variable suffice for all cases - no need to create multiple Q's

also please don't use i or j for loop index as your are shadowing their native role (i = j = sqrt(-1) for complex numbers)

clc
clearvars

y=1:1000;
for k=1:length(y)
    if y(k) <= 10
        Q(k)=1;
    elseif (y(k) > 10) && (y(k)<100)
        Q(k)=0.32*y(k)-2.2;
    else y(k) > 100
        Q(k) =300/sqrt(y(k));
    end  
end
loglog(y,Q)

Answer 3

[Rachna Singh]

Thank you everyone :)