How to fix: Index exceeds the number of array elements (4).

Hello, im write a coding to estimate the specific volume v of steam for the pressure range 0.01 through 10MPa and temperature range 400 degree Celcius through 1000 degree Celius using the ideal gas equation

but i got the error where it said "Index exceed the number of array elements(4) so I confuse about this error

fid = fopen('abc.txt','w');

Vact= [31.06300,40.29600,49.52700,58.75800;
      6.209400,8.057700,9.904700,11.75130;
      0.306610,0.401110,0.494380,0.587210;
      0.073430,0.098860,0.122920,0.146530;
      0.039958,0.055665,0.069856,0.083571;
      0.026436,0.038378,0.048629,0.058391];

P = [0.01,0.05,1,4,7,10];
T = [673.15,873.15,1073.15,1273.15];
	
	
for i=1:6
  for j=1:4
  vol(i,j) = ((0.000461631).*T(j))./P(i);
  end
end

% Calculate %error
	
for i=1:6
  for j=1:4
    error(i,j) = 100.0*(vol(i,j)-Vact(i,j))/Vact(i,j);
  end
end

[Star Strider]

The code you posted ran without error for me.

[SITI HASANAH]

i already try to fix it and can run it but didnt understand it said my variable "vol" appears to change size on every loop iteration(within a script), what should i do? is it ok to ignore it? how to solve this problem?

[Pulkit Goel]

You can make vol as a zeros matrix before starting that loop to remove that warning. It mostly helps with performance improvements.

vol = zeros(6,4);

You should be getting same warning with error variable. which can be removed in same way.

[Stephen23]

You definitely should NOT name any variable error, as this shadows the very important inbuilt error function.

[SITI HASANAH]

so it i should change variable error with other variable?

Answer 1

[Urmila Rajpurohith]

yes,you can replace the variable error with any other variable name;

The best suggestion is not to use inbuilt function names as variable names.

To check if any variable share a name with a built-in function you can use the which function.

For example :

>> error = 2;
>> which -all error
error is a variable.
C:\Program Files\MATLAB\R2020b\toolbox\matlab\connector2\logger\+connector\+internal\Logger.p  % Shadowed connector.internal.Logger method
C:\Program Files\MATLAB\R2020b\toolbox\simulink\dependency\analysis\@dependencies\error.p      % Shadowed dependencies method
built-in (C:\Program Files\MATLAB\R2020b\toolbox\matlab\lang\error)
% Shadowed

Hope this helps!