simple question function file syntax

function[root,ea,iter]=bisectt(func,xl,xu,es,maxit,varargin)
if nargin <3,
    disp('error')
end
    test=func(xl,varargin{:})*func(xu,varargin{:});
    if test>0,
        disp('error')
    end
if test>0,error('no sign change'),end
if nargin<4|isempty(es), es=0.0001;end
if nargin<5|isempty(maxit), maxit=50;end
iter = 0; xr = xl; ea = 10;
while (1)
xrold = xr;
xr = (xl + xu)/2;
iter = iter + 1;
if xr ~= 0,ea = abs((xr - xrold)/xr) * 100;end
test = func(xl,varargin{:})*func(xr,varargin{:});
if test < 0
xu = xr;
elseif test > 0
xl = xr;
else
ea = 0;
end
if ea <= es | iter >= maxit,break,end
end
root = xr;

I need to create another function file to calculate f(xl), f(xr), f(xu) how can i do that? the function is:

sqrt((9.81*x)/0.25)*tanh(sqrt((9.81*0.25)/x)*4)

thanks for your help!

Answer 1

[Michael Haderlein]

You can use anonymous functions:

f=@(x) sqrt((9.81*x)/0.25).*tanh(sqrt((9.81*0.25)./x)*4);

Then, f(xr) will return the respective value and f([xl xr xu]) will return all 3 values.

[B]

I'm still getting an erro. the syntax I'm using is wrong. can you provide me with the correct function file for sqrt((9.81*x)/0.25).*tanh(sqrt((9.81*0.25)./x)*4) that will evaluate the three variables xl,xu,xr

[Michael Haderlein]

Ah, you want an extra file for that. Then the syntax is just

 function res=myfunctionname(x)
 res=sqrt((9.81*x)/0.25).*tanh(sqrt((9.81*0.25)./x)*4);

Put this in a file named myfunctionname.m, that's all.

Answer 2

[Walter Roberson]

f=@(x) sqrt((9.81*x)/0.25).*tanh(sqrt((9.81*0.25)./x)*4);
[A,B,C] = bisectt(f, -10, 10);

to do the calculation over -10 to +10