Fix Origin of R Plot Axes at Zero

Standard R plots does not set the origin of the x and y axis at zero. To reset this parameter so that the origin of the plot is fixed at 0,0 simply use the xaxs and yaxs parameters. Here is a description from the R graphical parameters help page.

The style of axis interval calculation to be used for the x-axis. Possible values are "r", "i", "e", "s", "d". The styles are generally controlled by the range of data or xlim, if given.
Style "r" (regular) first extends the data range by 4 percent at each end and then finds an axis with pretty labels that fits within the extended range.
Style "i" (internal) just finds an axis with pretty labels that fits within the original data range.
Style "s" (standard) finds an axis with pretty labels within which the original data range fits.
Style "e" (extended) is like style "s", except that it is also ensures that there is room for plotting symbols within the bounding box.
Style "d" (direct) specifies that the current axis should be used on subsequent plots.
(Only "r" and "i" styles have been implemented in R.)

Finally, here is a brief example code snippet to demonstrate how the syntax works.