"Function might be unused"

I can't seem to figure our why Matlab doesn't like my function. It keeps telling me that it is probably called incorrectly but I can't see what I did wrong here.

   Ideal Boiler Function

hfg=930

lhv=21500

p_percent=100

p=p_percent/100

MFfr=0.5191

%This function will calculate the steam mass flow rate (SMfr)

%of an actual boiler with 100% efficency (p_percent=100%)

%This funtion has 4 inputs (p,hfg,lhv,and MFfr),

%and 1 output (SMfr).

function SMfr=Ideal_Boiler(p,hfg,lhv,MFfr)

      SMfr=(MFfr*p*lhv)/hfg;

      output=SMfr;

end

disp('SMfr =');disp(SMfr)

Answer 1

[bio lim]

I don't see any problems, unless you defined the function inside your main script, and MATLAB doesn't allow that.

hfg=930;
lhv=21500;
p_percent=100;
p=p_percent/100;
MFfr=0.5191;

SMfr=Ideal_Boiler(p,hfg,lhv,MFfr)
disp('SMfr =');disp(SMfr)

SMfr =

     12.0007

SMfr =
   12.0007

[Shelby Russ]

Um. So, how do I know if it is defined in the main script? I just opened one and saved my file as the function name and it hates me for it. I'm so confused.

[bio lim]

You need a two .m files, one for your function and one for your main program.

In one of them, you declare your function as:

function SMfr=Ideal_Boiler(p,hfg,lhv,MFfr)
      SMfr=(MFfr*p*lhv)/hfg;
      output=SMfr;
end

And in your main program, you actually use the values, and call for your function:

hfg=930
lhv=21500
p_percent=100
p=p_percent/100
MFfr=0.5191

SMfr=Ideal_Boiler(p,hfg,lhv,MFfr) % calling Ideal_Boiler function

And the output is:

SMfr =
     12.0007

[Shelby Russ]

Oh my gosh, thank you so much. I would have never figured that out.

[bio lim]

My pleasure. One more thing:

In your code, if you end a line with a semi-colom, i.e., ; , MATLAB doesn't print out the results. So in your code:

disp('SMfr =');disp(SMfr)

Is unnecessary, if you just end your function call, i.e., SMfr=Ideal_Boiler(p,hfg,lhv,MFfr) without a semi-colon (Meaning it will print the result out).

Answer 2

[Kevin Agudo]

syms t
function y = f(t)
t=linspace(0,100);
f(x)=(3*t^2+1)./(t^3+50);
h=.01;
plot(t ,(f(t+h)-f(t))./h,t,(f(t+h)-2*f(t)+f(t-h))/h^2)
end

When I run the function, dont get a graph and it says "function f may not be used"

[Walter Roberson]

h=.01;
t=linspace(0,100);
plot(t ,(f(t+h)-f(t))./h,t,(f(t+h)-2*f(t)+f(t-h))/h^2)

function y = f(t)
y=(3*t.^2+1)./(t.^3+50);
end