function linesquare()
x=input('input x:');
y=input('input y:');
b=input('input b:');
clf reset
set(gcf,'unit','normalized')
axes('position',[0.1,0.1,0.8,0.8],'xlim',[0,1],'ylim',[0,1]);
x1=(x-b/2):0.01:(x+b/2);
y1=(y+b/2)*ones(size(x1));
x2=(x-b/2):0.01:(x+b/2);
y2=(y-b/2)*ones(size(x2));
line(x1,y1);line(x2,y2);
y3=(y-b/2):0.01:(y+b/2);
x3=(x-b/2)*ones(size(y3));
y4=(y-b/2):0.01:(y+b/2);
x4=(x+b/2)*ones(size(y4));
line(x3,y3);line(x4,y4);