My 'fminsearch' optimization function in Matlab isn't running. the output value doesn't change, just keeps showing the same value. What's going wrong?

I need to optimize a particular value in a function (Which acts as my objective function), but it doesn't work. In my objective function,I'm calling another function, and the output of that, acts as the input to my main equation which has to be minimized. Is there something wrong that I've done. Here's the code for the objective function, followed by the main program.

function Y = obj_fun(alp) % Objective Function

load input_acc

%Input values for the Function to compute ODI

wn = 1; eta = 0.02; alpha = 0.041945; Fy = 37.847453; gama = 1/2; beta = 1/4; du = 0.226179; dy = 0.020004; k_in = 1891.997954;

signal_new = alp*X_Norm; %' alp' is the function handle in the anonymous function

[~,~,~, ODI ] = test_Newmark_Beta_Nonlin(wn,eta,alpha,Fy,signal_new,gama,beta,du,dy,k_in);

%ODI, which I get from the above function, is the input parameter to Y, which I need to minimize

Y = (0.4 - ODI).^2; %While Y tends to zero, I need alpha_fn to be optimized.*

return

Main Program to find Critical Acceleration

alpha_in = ones(1,32)*10; %Initial Guess

alpha_fn = fminsearch(@(alp) obj_fun(alp),alpha_in); %fminsearch on objective function

signal_fn = alpha_fn*X_Norm; %Using the optimized value of alpha_fn here

[X,Xdot,Xddot,ODI] = test_Newmark_Beta_Nonlin(wn,eta,alpha,Fy,signal_fn,gama,beta,du,dy,k_in);

ODI(end) %Checking whether ODI value has been maximized

[Torsten]

Where do you define X_Norm ? Is it a scalar or a vector ?

Is ODI a scalar or a vector (it should be a scalar) ?

Best wishes

Torsten.