Variable Variation over the same range

Hi everyone,

as a MatLab rookie I need your help! I´m working on a programm, where different variables shall assume certain values of a given range. I would like to achieve that these different variables assume values indipentently from each other even though the range is the same. This means, that I need to calculate all possible versions (i.e. where lam_o_p = 35, lam_i_p = 25 and lam_i_c = 40 or where lam_o_p = 30, lam_i_p = 30 and lam_i_c = 35).

%Span [m]

span=3.5:0.5:7;

%Number of lamellas [-]

lam=3:2:7;

%Depth outer lamella parallel to span [mm]

lam_o_p=20:5:50

%Depth inner lamella parallel to span [mm]

lam_i_p=20:5:50;

%Depth inner lamella cross to span [mm]

lam_i_c=20:5:50;

%Calculation of total depth [mm]

if(lam>5)

depth_tot_7=lam_o_p*4+lam_i_p*2+lam_i_c

else

0

I´m looking forward to your answers.

Thanks in advance

Answer 1

[Steve Eddins]

I am interpreting your question this way: you would like to compute depth_tot_7 for all possible combinations of the different values of lam_o_p, lam_i_p, and lam_i_c.

Here are two different methods.

Using ndgrid

lam_o_p=20:5:50;
lam_i_p=20:5:50;
lam_i_c=20:5:50;

[LOP,LIP,LIC] = ndgrid(lam_o_p,lam_i_p,lam_i_c);
size(LOP)

ans =

     7     7     7

% Calculate total depth for all possible combinations of LOP, LIP, and
% LIC.
depth_tot_7 = LOP*4 + LIP*2 + LIC;
size(depth_tot_7)

ans =

     7     7     7

Using implicit expansion

This method requires less memory and is usually faster than the ndgrid method.

lam_o_p = 20:5:50;     % row vector
lam_i_p = (20:5:50)';  % column vector 
lam_i_c = reshape(20:5:50,1,1,[]);  % vector along 3rd dimension

depth_tot_7 = lam_o_p*4 + lam_i_p*2 + lam_i_c;
size(depth_tot_7)

ans =

     7     7     7

For more information on MATLAB behavior when performing arithmetic on operands with different sizes, see "Compatible Array Sizes for Basic Operations."

[Davide Bertoldi]

Hello Steve,

firstly I want to thank you for your rapid answer, but unfortunately due to my bad explanation it is not exactly what I need. So let me try again (see also the modified code below): if the first logical expression is correct, depth_tot_7 will be calculated. If not, the (if correct) next logical check calculates depth_tot_5 or depth_tot_3. What I want to achieve are the following two things:

a) I want to define a range from 3, 5, 7 for lam without having to specify one of these values at the beginning.

b) If lam=3, I would like the program to combine all of the possible lamella depths that are contained in the regarding formula. This means that I´d like my programm to create total depths where lamellas have different attributed depths (for lam = 3 i.e. 25*2+50, 35*2+20, 50*2+35, 45*2+50 etc.). I would like to achieve that the values are differently combined to each other, considering the fact that these single lamellas have the same range and steps.

I hope that my explanation is now better and looking forward to your answer and help.

Best regards

%Spannweite [m]
span=3.5:0.5:7;

%Number of lamellas [-]
lam=3

%Depth outer lamella parallel to span [mm]
lam_o_p=20:5:50;

%Depth inner lamella parallel to span [mm]
lam_i_p=20:5:50;

%Depth inner lamella cross to span [mm]
lam_i_c=20:5:50;

%Calculation of total depth [mm]
if(lam>5)
    depth_tot_7=lam_o_p*4+lam_i_p*2+lam_i_c
elseif (lam>3)
    depth_tot_5=lam_o_p*2+lam_i_p*1+lam_i_c
else
    depth_tot_3=lam_o_p*2+lam_i_c
end

[Steve Eddins]

The question is still not perfectly clear to me, but perhaps you could create a function that would take lam as the input argument and return depth_tot. It might look something like this:

function depth_tot = my_fcn(lam)
%Depth outer lamella parallel to span [mm]
lam_o_p=20:5:50;
%Depth inner lamella parallel to span [mm]
lam_i_p=20:5:50;
%Depth inner lamella cross to span [mm]
lam_i_c=20:5:50;
%Calculation of total depth [mm]
if(lam>5)
    depth_tot=lam_o_p*4+lam_i_p*2+lam_i_c
elseif (lam>3)
    depth_tot=lam_o_p*2+lam_i_p*1+lam_i_c
else
    depth_tot=lam_o_p*2+lam_i_c
end

Then you could call your function like this:

lam_range = 3:0.5:7;
for k = 1:length(lam_range)
    D(k,:) = my_fcn(lam_range(k));
end