// the important line is this:
frame::current().y1axis()->pos(x1len(0));  // put y axis at 0 position
frame::current().x1axis()->pos(y1len(2));  // put y axis at 0 position

// plot something else
frame::current().draw_frame(false); // do not draw the rectangular frame
set::xrange(-10,10);
set::xtitle("X values");
set::ytitle("Y values");
plot(_1,_1*sin(_1)+2);

The position of an axis can be changed from its default value (either side of a frame) using the following function:

void axis::pos(const length &);

Note that this function does not expect a numeric value, which would set the position of the axis along, say, the x1 axis. It expects an argument of type length, because this is more generic: one can for example position the y1 axis to the 0-value on the x1 axis as in the example above.

Source files:
   axis.h
   axis.cc