Intergrating the data using a scalar value

Hello,

I am trying to do integration of a excel data. When I try to do that I am getting an error as follows:

Error using cumtrapz (line 51)

Dimension argument must be a positive integer scalar within indexing range.

Please can someone help me in solving that .

My code:

X1 = xlsread('Abb76at104.xlsx','A1:A63');

Y1 = xlsread('Abb76at104.xlsx','B1:B63');

V = 40.020;

A1 = pi*(X1).^2;

Q1 = A1.*Y1;

Int1 = cumtrapz(A1, V);

X2 = xlsread('Abb76at104.xlsx','A64:A130');

Y2 = xlsread('Abb76at104.xlsx','B64:B130');

A2 = pi*(X2).^2;

Q2 = (A2).*40.02;

Int2 = cumtrapz(A2, V);

Thanks in advance.

Answer 1

[Mathieu NOE]

hello

see the doc for cumtrapz

I believe you simply put the arguments in the wrong order

it must be

Int1 = cumtrapz(V,A1);

and

Int2 = cumtrapz(V,A2);

[Vishnuvardhan Naidu Tanga]

Hello @Mathieu NOE,

Thank you for the response. But I need to integrate A1 and A2 with respect to V. But not the other way around.

[Mathieu NOE]

what is V ?

this is a scalar so I take it for the x step - see documentation of cumtrapz

if you stick to your code I don't understand how you ca integrate a single scalar , the second argument of cumtrapz is the vector to integrate (and not vice versa)

[Vishnuvardhan Naidu Tanga]

V is velocity. Is there any way to turn that scalar value to a vector?

[Mathieu NOE]

well , please explain a bit your code and the goal

what are X1 and Y1 ? how is the time increment defined ?

so far I am just guessing :

• X1 is a radius, so A1 would be a section (area? ), Q1 is a volumetric flow (?) and you want to do a time integration of that to have a total volume in a given time interval ?
• so what we need to do is to define the time step ; waht is the time increment in your data ?
• why is V a scalar ?
• also I dont understand the difference between the computation on X1, Y1 and X2, Y2 on the other side
• I don't get why Q1 and Q2 are not computed in a similar manner :

X1 = xlsread('Abb76at104.xlsx','A1:A63');

Y1 = xlsread('Abb76at104.xlsx','B1:B63');

V = 40.020;

A1 = pi*(X1).^2;

Q1 = A1.*Y1;

Int1 = cumtrapz(V,A1);

X2 = xlsread('Abb76at104.xlsx','A64:A130');

Y2 = xlsread('Abb76at104.xlsx','B64:B130');

A2 = pi*(X2).^2;

Q2 = (A2).*40.02;

Int2 = cumtrapz(V,A2);

[Vishnuvardhan Naidu Tanga]

Now I understood. I thought that we can do integration using a scalar. but i dont think it is possible. And Q is flowrate which i am just verifying. It makes nothing in the computation. The increment is just random. And I want to integrate the data at constant velocity. so i kept the V constant. But I think it doesnt make any sense. Thank you for clarifying.

[Mathieu NOE]

my pleasure !

if Q is your flow rate , and t is time vector or dt = time increment, you can integrate Q vs time

by doin either cumtrapz(t,Q); or cumtrapz(dt,Q);

[Vishnuvardhan Naidu Tanga]

Thank you once again for sorting the thing out. Have a nice day.

[Mathieu NOE]

my pleasure (again) !