I am receiving an error message that there are not enough input arguments in my function f.

function [f, g] = rosenbrock(x)
f = sum((1 - x(1:end-1)).^2 + 100*(x(2:end) - x(1:end-1).^2).^2);
g = zeros(size(x));
g(1) = -400*x(1)*(x(2) - x(1)^2) - 2*(1 - x(1));
g(2:end-1) = 200*(x(2:end-1) - x(1:end-2).^2) - 400*x(2:end-1).*(x(3:end) - x(2:end-1).^2) - 2*(1 - x(2:end-1));
g(end) = 200*(x(end) - x(end-1)^2);
end
function [f, g] = exponential(x)
f = -exp(-0.5*sum(x.^2));
g = -x.*exp(-0.5*sum(x.^2));
end

[John D'Errico]

How are you trying to use f?

[Josh]

As a representation of a rosembrock function

Answer 1

[Walter Roberson]

Looks to me as if it works

format long g
x = randn(1,10)

x = 1×10

-0.371911875404682 -0.313989043713682 -0.281367533926339 0.280508079780121 1.02217448547427 -0.544894220859205 -1.47050086682099 -0.617560248626988 -0.196573116936724 -0.0818487640582806

[f1, g1] = rosenbrock(x)

f1 = 
          1519.03045345865

g1 = 1×10

1.0e+00 * -70.0312340180861 -140.810365957436 -55.8938060907731 -67.0334996273034 838.736870722702 -706.257492462287 -1993.58070016789 -701.990241527909 -127.457920387497 -24.0979508720999

[f2, g2] = exponential(x)

f2 = 
         -0.11500242683972

g2 = 1×10

0.0427707682420501 0.0361095020281565 0.0323579492354364 -0.0322591099228638 -0.117552546483183 0.0626641577697472 0.169111168354326 0.0710209273118448 0.0226063854991714 0.00941280650053396

function [f, g] = rosenbrock(x)
f = sum((1 - x(1:end-1)).^2 + 100*(x(2:end) - x(1:end-1).^2).^2);
g = zeros(size(x));
g(1) = -400*x(1)*(x(2) - x(1)^2) - 2*(1 - x(1));
g(2:end-1) = 200*(x(2:end-1) - x(1:end-2).^2) - 400*x(2:end-1).*(x(3:end) - x(2:end-1).^2) - 2*(1 - x(2:end-1));
g(end) = 200*(x(end) - x(end-1)^2);
end
function [f, g] = exponential(x)
f = -exp(-0.5*sum(x.^2));
g = -x.*exp(-0.5*sum(x.^2));
end

Answer 2

[Image Analyst]

You're probably just clicking the green run triangle button. Doing that does not "invent" some x to pass in to the function. You have to define x somehow and then call your rosenbrock function from the command line or a script, like

x = rand(1,10);
[f, g] = rosenbrock(x);