How to show an image in Matlab

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MatLab

image-processing

Hello everyone, I have a assignment. Actually not an importatn course for me. I want to develop myself at .Net. Whatever, I am doing a matlab assignment I completed many parts. But I am taking some error messages. For example, when I insert show_img(parameters) I am taking show_img is undefined(or something like this)
When I made research I learned that; I should insert this fucntion but I have no idea about this. So could you show me some ways, could you help me ?

The actual error message : Undefined function or method 'show_img' for input arguments of type 'double'.

function [ph] = show_img(img, figno, scaled, map)
%SHOW_IMG display an image with possible scaling
% usage: ph = show_img(img, figno, scaled, map)
% img = input image
% figno = figure number to use for the plot
% if 0, re-use the same figure
% if omitted a new figure will be opened
% optional args:
% scaled = 1 (TRUE) to do auto-scale (DEFAULT)
% not equal to 1 (FALSE) to inhibit scaling
% map = user-specified color map
% ph = figure handle returned to caller
%----

I should complete this function.