Why does this error occur-Unrecognized function or variable 's'.

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Zoe Westcott 2022-6-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1746675-why-does-this-error-occur-unrecognized-function-or-variable-s

回答： Siraj 2023-9-14

function[e]= Convergent(h,m,s)
A= (32*pi)/7 ;
f =  @(x) 0.*( x<25/64 & x>39/64) +cos(A*(x-0.5)).*( (25/64)<=x & x<=39/64);
g = @(x) 0.*( x<25/64 & x>39/64) +-A*sin(A*(x-0.5)).*( (25/64)<=x & x<=39/64);
x = 0:h:1;  
n = length(x);
y=(f(x)).^m;
z=g(x).*m.*(f(x).^(m-1));
dy = zeros(n,1); % preallocate derivative vectors
if s==1
  % 1st order(central)
  for i=2:n-1
    dy(i) = (y(i+1)-y(i))/(h);
  end
elseif s==2
  % 2nd order(central)
  for i=2:n-1
    dy(i) = (y(i+1)-y(i-1))/(2*h);
  end
  % 3rd order(forward)
  elseif s==3
   for i=2:n-1
    dy(i) = ((-11/6)*y(i)+3*y(i+1)-(3/2)*y(i+2)+(1/3)*y(i+3))/(h) ;
   end
  % The error function 
  e=max(abs(z-dy')); 
end

I'm trying to define the function called convergent for determining order of convergent. When I run this code it says "Unrecognized function or variable 's'.". Where s is a imput value depending om what order of derivative i want to use. Thanks.

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dpb 2022-6-23

编辑：dpb 2022-6-23

在 MATLAB Online 中打开

I reformatted the code to ensure my eyes weren't lying -- that shows the closing end of the if...end construct is missing before the line computing e

As for the error message about s, that would have to be from somewhere else in the attempted invocation of the function it would appear; we need to see the exact code and error in context to be able to know for sure.

It looks as though

 ...
 elseif s==3
   for i=2:n-1
    dy(i) = ((-11/6)*y(i)+3*y(i+1)-(3/2)*y(i+2)+(1/3)*y(i+3))/(h) ;
   end
  end
  % The error function 
  e=max(abs(z-dy')); 
  end

was intended.

Torsten 2022-6-23

How do you call the function "Convergent" ?

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Answer 1

Siraj 2023-9-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1746675-why-does-this-error-occur-unrecognized-function-or-variable-s#answer_1310001

在 MATLAB Online 中打开

Hi! It is my understanding that the error appears due to a missing "end" statement to close the "if" statement in the code. By adding the necessary "end" statement, the code was able to run successfully without any errors.

To learn more about how to properly close an "if" block in MATLAB, you can refer to the following link:

https://www.mathworks.com/help/matlab/ref/if.html

Attaching the code for your reference.

Temp = Convergent(1,1,1);
disp(Temp)
     0
function[e]= Convergent(h,m,s) 
A= (32*pi)/7 ; 
f =  @(x) 0.*( x<25/64 & x>39/64) +cos(A*(x-0.5)).*( (25/64)<=x & x<=39/64); 
g = @(x) 0.*( x<25/64 & x>39/64) +-A*sin(A*(x-0.5)).*( (25/64)<=x & x<=39/64); 
x = 0:h:1;   
n = length(x); 
y=(f(x)).^m; 
z=g(x).*m.*(f(x).^(m-1)); 
dy = zeros(n,1); % preallocate derivative vectors 
if s==1 
  % 1st order(central) 
  for i=2:n-1 
    dy(i) = (y(i+1)-y(i))/(h); 
  end 
elseif s==2 
  % 2nd order(central) 
  for i=2:n-1 
    dy(i) = (y(i+1)-y(i-1))/(2*h); 
  end 
  % 3rd order(forward) 
elseif s==3 
   for i=2:n-1 
    dy(i) = ((-11/6)*y(i)+3*y(i+1)-(3/2)*y(i+2)+(1/3)*y(i+3))/(h) ; 
   end 
end 
  % The error function  
  e=max(abs(z-dy'));  
end 

However, the error that you have attached suggests that the variable 's' has not been defined or is not accessible within the scope of your code. To avoid the "Unrecognized function or variable 's'" error, ensure that you pass a valid value for 's' when calling the 'convergent' function. Also, double-check that you haven't accidentally overwritten the variable 's' elsewhere in your code.

Hope this helps.