Plotting the boundaries of an object

I read that the syntax f plotting a boundary of an object is the following:

plot (t(:,2),t(:,1),'g','Linewidth',2)

where t is a boundary. I ran it in MATLAB and it worked. However I did not know why we input the first two arguments in that manner.

Can any share his knowledge about that?

Thanks for your time and attention

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/techdoc/ref/plot.html

plot(X1,Y1,...,Xn,Yn) plots each vector Yn versus vector Xn on the same axes.

http://www.mathworks.com/help/techdoc/math/f1-85462.html#f1-85544

Accessing Multiple Elements

For the 4-by-4 matrix A shown below, it is possible to compute the sum of the elements in the fourth column of A by typing

A = magic(4);
A(1,4) + A(2,4) + A(3,4) + A(4,4)
You can reduce the size of this expression using the colon operator. Subscript expressions involving colons refer to portions of a matrix. The expression

A(1:m, n)
refers to the elements in rows 1 through m of column n of matrix A. Using this notation, you can compute the sum of the fourth column of A more succinctly:

sum(A(1:4, 4))

Thus, the syntax you are using is to extract columns from your array and use them as the X and Y for plotting purposes.

[Said Rahal]

Thank you Walter. So Can I conclude that by definition the second column of the matrix that defines a boundary is X and the first column is Y.

[Walter Roberson]

In that matrix, yes. Not generally in matrices, though.