set-frame-width

set-frame-width is a built-in function in `C source code'.

(set-frame-width FRAME WIDTH &optional PRETEND PIXELWISE)

Set width of frame FRAME to WIDTH columns.
Optional third arg PRETEND non-nil means that redisplay should use WIDTH
columns but that the idea of the actual width of the frame should not
be changed.

Optional fourth argument PIXELWISE non-nil means that FRAME should be
WIDTH pixels wide. Note: When `frame-resize-pixelwise' is nil, some
window managers may refuse to honor a WIDTH that is not an integer
multiple of the default frame font width.