Please check my Matlab code!!!??

I have 2 set of data (crank angle and pressure). I upload into Workspace. http://www.flickr.com/photos/52175884@N08/8618031267/in/photostream The left column is the Crank Angle, the right column is the Pressure.

But I need to find the plot of Pressure vs Volume. The formula of Volume is given by http://www.flickr.com/photos/52175884@N08/8616297620/in/photostream

I need to write a code, such that the plot of Pressure and volume will shown. Please check my code. http://www.flickr.com/photos/52175884@N08/8619138098/in/photostream

[Tobias]

Could you specify the error you are getting?

[J K]

http://www.flickr.com/photos/52175884@N08/8619188684/in/photostream See the link.

[Jan]

It is very tedious to follow a bunch of links. Other people post their code and error messages directly by copy&paste. This would be more friendly for the readers.

[J K]

@Jan Simon, this is my code.

Vd=1.236699e-4 r=10 R=3

V=(Vd/(r-1))+(Vd/2)*(1+R-cos(data(:,1))-(R^2-sin(data(:,1)).^2)^0.5) plot (V(:,1), data(:,2)), xlabel('CA'),ylabel('Pressure')

Since I already have the set of data for crank angle, hence, I substitute the value of theta in Equation with data(:,1). The data(:,1) means all row, first column(left column).

But when I write in the matlab command window, it show ??? Error using ==> mpower Inputs must be a scalar and a square matrix.

How to solve? I follow the instruction by Image Analyst, but it is still showing the same error.

[Jan]

Please follow the "? Help" link to learn how to format code.

Answer 1

[Image Analyst]

When you square arrays, use ".^2" instead of "^2" - if you use the dot it will do an element by element squaring (each element is squared) otherwise it's a matrix multiplication which is totally different.

[J K]

Hi, I follwed what you said, but the error still the same.

how to solve?

[Matt Kindig]

You also need to use ".^0.5" instead of "^0.5".

Can you post your updated code?

[J K]

I load a file (E.dat). The file has 2 column, left column is Crank angle, right column is Pressure. This is my code.

load E.dat;
CA = E(:,1);
Pressure = E(:,2);

plot(CA,Pressure); 
xlabel('CA (Deg)');
ylabel('Pressure (Bar)');
title('Graph of Pressure vs CA')

Vd=1.236699e-4
r=10
R=3

V=(Vd/(r-1))+(Vd/2)*(1+R-cos(CA)-(R^2-(sin(CA).^2))^0.5);
plot (V, Pressure), xlabel('Volume'),ylabel('Pressure')

The part that I don't get is the equation part.

[Image Analyst]

Like Matt told you:

V=(Vd/(r-1))+(Vd/2)*(1+R-cos(CA)-(R^2-(sin(CA).^2)).^0.5);

[J K]

Thank you.

One more thing, the unit of Pressure is given in Bar. How can I change it into kPa in the code, or the graph?

[J K]

I know 1 Bar = 100kPa. But how to write that?