set Emacs frame size according to resolution dynamically

gistfile1.txt

(defun set-frame-size-according-to-resolution ()
  (interactive)
  (if window-system
	  (progn
		(setq width-chars (/ (/ (x-display-pixel-width) (frame-char-width)) 2))
		(setq height-lines (- (/ (x-display-pixel-height) (frame-char-height)) 3))
		(setq default-frame-alist
			  `((top . 0) (left . 0)
				(width . ,width-chars)
			(height . ,height-lines)))
		(if (> (x-display-pixel-width) 1500)
			;; or Monaco, Bitstream Vera Sans Mono, Liberation Mono
			;; (add-to-list 'default-frame-alist '(font . "PragmataPro-14"))
			(add-to-list 'default-frame-alist '(font . "Input Mono Compressed-14"))
		  (add-to-list 'default-frame-alist '(font . "Input Mono Compressed-13")))
		))
  ;; the following two settings are specifically for afternoon-theme
  ;; the combination colors of highlighted line and comments
  ;; (custom-set-faces
  ;;  '(font-lock-comment-face
  ;;	 ((t (:foreground "gray60" :slant italic :weight normal :family "Menlo")))
  ;;	 ))
  ;; (set-face-background 'highlight "gray30")
  )