Different variable in function

function s=traorl(fun,a,b,M)
h=(b-a)/M
s=0
for k=1:(M-1)
x=a+k*h
s=s+feval(fun,x)    
end
s=h*(feval(fun,a)+feval(fun,b))/2+h*s
end
%% I wants to run function as a variable x and as well as other variables like  I use function, 'fun=q*t*exp(-x)'. where i use second script file as
for x=linspace(0,10);
fun=inline('q*t*(exp(-x))');
B=traorl(fun,0,1,10)
end 

But when I try to run this then i found error as

'Error using inline/feval (line 22)
Not enough inputs to inline function'
Error in traorl (line 6) 
s=s+feval(fun,x) 
Error in Untitled (line 7)
B=traorl(fun,0,1,10)

Answer 1

[Walter Roberson]

inline('q*t*(exp(-x))')

will not pay any attention to the current value of x in the workspace -- and there is no q or t in the workspace for it to ignore.

That inline() call is going to create an inline function that expects 3 inputs in the order q, t, x .

You then attempt to feval() the function of three variables, passing in only a single variable.

We can guess that what you want is

syms q t
fun = @(x) q * t * exp(-x);
B=traorl(fun,0,1,10);

which will give a result such as B = (113967594646290279*q*t)/180143985094819840 . However, this pays no attention to the linspace(0,10) you are talking about.

There seems to be some confusion as to what x is. Is it the linspace value within the loop, but inside traorl it is to take on the role of what is q outside the loop ??

[SHARAD KUMAR UPADHYAY]

Thanks for your kind reply, This might be helpful for me.

[SHARAD KUMAR UPADHYAY]

syms q t
for x=0:10;
fun=@(x) q*(exp(-x));
B=traorl(fun,0,1,10);
end

%%The problem of different variables q, t are solved but there is
%  another problem for values of
%% given in range 0:10, but i am getting only one value of B, as i
%  give more than one value of x

.

[Walter Roberson]

fun=@(x) q*(exp(-x));

tells MATLAB that at the time of the assignment, to look in the workspace to find the current value of q (the value right then) and take a copy of that, and to construct a function of with one dummy parameter named x designating the parameter passed in at the time of execution. When fun is executed, the remembered value of q will be recalled (no matter what q might have been assigned in the mean time, the remembered q will be used), and the passed in value will be used each place that x is mentioned.

This process ignores the value of x in the workspace due to the for x statement.

You are also overwriting the value of B each iteration through the loop.

syms q t
for AVariableUsedOnlyAsAnIndex=0:10
    FunctionThatDoesNotChangeWithIndexValue = @(AVariableThatHasNothingToDoWithTheIndexVariable) q*(exp(-AVariableThatHasNothingToDoWithTheIndexVariable));
    B(AVariableUsedOnlyAsAnIndex+1) = traorl(FunctionThatDoesNotChangeWithIndexValue, 0, 1, 10);
end

and equivalent:

syms q
FunctionThatDoesNotChangeWithIndexValue = @(AVariableThatHasNothingToDoWithTheIndexVariable) q*(exp(-AVariableThatHasNothingToDoWithTheIndexVariable));
for AVariableUsedOnlyAsAnIndex=0:10
   B(AVariableUsedOnlyAsAnIndex+1) = traorl(FunctionThatDoesNotChangeWithIndexValue, 0, 1, 10);
end

and equivalent:

syms q
FunctionThatDoesNotChangeWithIndexValue = @(AVariableThatHasNothingToDoWithTheIndexVariable) q*(exp(-AVariableThatHasNothingToDoWithTheIndexVariable));
B(1:length(0:10)) = traorl(FunctionThatDoesNotChangeWithIndexValue, 0, 1, 10);

[SHARAD KUMAR UPADHYAY]

Dear sir,

Answer given is very helpful for me. Another thing is, How can I do the double integration by this program? As for eg. I have function 'fun=@(x,y) q*t*sinh(y)*exp(-x). If this program is not right then please tell me the improvements in this program.

%%

function s=traorl(fun,a,b,M)

h=(b-a)/M

s=0

for k=1:(M-1)

x=a+k*h

s=s+feval(fun,x)

end

s=h*(feval(fun,a)+feval(fun,b))/2+h*s

end

Answer 2

[SHARAD KUMAR UPADHYAY]

Dear sir,

Answer given is very helpful for me. Another thing is, How can I do the double integration by this program? As for eg. I have function 'fun=@(x,y) q*t*sinh(y)*exp(-x). If this program is not right then please tell me the improvements in this program.