Re: indentation problem II

[Arash Esbati]

Hi Keita,

Ikumi Keita <ikumi@ikumi.que.jp> writes:

>>>>>> Uwe Brauer <oub@mat.ucm.es> writes:
>> That seems to me also a strange result.
>
> It seems to me an ordinary result in array environment, "&" signs are
> vertically aligned. What other result do you expect?
>
>> \begin{equation}\label{Mn}
>>   \begin{array}{rcl}
>>     \lim_{n\rightarrow\infty} M^n &=& \lim_{n\rightarrow\infty} PJ^nP^{-1} \\
>>     \\
>>                                 &=& 
>>                                     \begin{pmatrix}
>>                                       1 & 1 \\
>>                                       0 & \tfrac{999}{10} \\
>>                                     \end{pmatrix}
>>                                     \begin{pmatrix}
>>                                       e^{-100t} & 0 \\
>>                                       0 & e^{-\tfrac{t}{10}} \\
>>                                     \end{pmatrix}
>>                                     \begin{pmatrix}
>>                                       1 & -\tfrac{10}{999} \\
>>                                       0 & \tfrac{10}{999} \\
>>                                     \end{pmatrix} \\
>>     \\
>>                                 &=& 
>>                                     \begin{pmatrix}
>>                                       e^{-100t} & 
>> \tfrac{10}{999}(e^{-\tfrac{t}{10}} - e^{-100t}) \\
>>                                       0 & e^{-\tfrac{t}{10}} \\
>>                                     \end{pmatrix}
>>   \end{array}
>> \end{equation}
>> \end{document}

Hitting 'M-RET' in a pmatrix inserts only the line break \\ and not any
ampersands.  I don't use these environments so I have no experience
about what is convenient, but what do think about this change?  Is it an
improvement?

--8<---------------cut here---------------start------------->8---
diff --git a/style/amsmath.el b/style/amsmath.el
index 5e7812e7..8f1eb030 100644
--- a/style/amsmath.el
+++ b/style/amsmath.el
@@ -57,7 +57,13 @@
     "align*" "gather*" "flalign*" "multline*" "equation*"
     "split"
     "cases"
-    "matrix" "smallmatrix" "pmatrix" "bmatrix" "Bmatrix" "vmatrix" "Vmatrix"
+    '("matrix" LaTeX-amsmath-env-matrix)
+    '("smallmatrix" LaTeX-amsmath-env-matrix)
+    '("pmatrix" LaTeX-amsmath-env-matrix)
+    '("bmatrix" LaTeX-amsmath-env-matrix)
+    '("Bmatrix" LaTeX-amsmath-env-matrix)
+    '("vmatrix" LaTeX-amsmath-env-matrix)
+    '("Vmatrix" LaTeX-amsmath-env-matrix)
     "subequations"
     '("subarray" "Alignment"))

@@ -126,13 +132,13 @@
                    ("alignedat" . LaTeX-item-equation-alignat)
                    ("flalign"  . LaTeX-item-equation)
                    ("flalign*" . LaTeX-item-equation)
-                   ("matrix" .  LaTeX-item-equation)
-                   ("pmatrix" .  LaTeX-item-equation)
-                   ("bmatrix" .  LaTeX-item-equation)
-                   ("Bmatrix" .  LaTeX-item-equation)
-                   ("vmatrix" .  LaTeX-item-equation)
-                   ("Vmatrix" .  LaTeX-item-equation)
-                   ("smallmatrix" . LaTeX-item-equation)
+                   ("matrix" .  LaTeX-item-equation-matrix)
+                   ("pmatrix" .  LaTeX-item-equation-matrix)
+                   ("bmatrix" .  LaTeX-item-equation-matrix)
+                   ("Bmatrix" .  LaTeX-item-equation-matrix)
+                   ("vmatrix" .  LaTeX-item-equation-matrix)
+                   ("Vmatrix" .  LaTeX-item-equation-matrix)
+                   ("smallmatrix" . LaTeX-item-equation-matrix)
                    ("subarray" . LaTeX-item-equation)
                    ("cases"    . LaTeX-item-equation))
                  LaTeX-item-list))
@@ -246,6 +252,41 @@ START and END."
   (let ((num (string-to-number (buffer-substring-no-properties start end))))
     (if (integerp num) (+ num num -1))))

+(defun LaTeX-amsmath-env-matrix (env)
+  "Insert matrix ENV with one ampersand."
+  (LaTeX-insert-environment env)
+  (LaTeX-item-equation-matrix t))
+
+(defun LaTeX-item-equation-matrix (&optional suppress)
+  "Insert contents to terminate a line in matrix environments.
+Put line break macro on the last line and insert suitable number
+of ampersands if possible.  This number is extracted from the
+first line of the environment.
+
+If SUPRESS is non-nil, do not insert a line break and only one
+single ampersand. "
+  (if suppress
+      (save-excursion (insert "&"))
+    (end-of-line 0)
+    (just-one-space)
+    (TeX-insert-macro "\\")
+    (forward-line 1)
+    (indent-according-to-mode)
+    (let* ((p (point))
+           (s (save-excursion
+                (LaTeX-find-matching-begin)
+                (point)))
+           (e (save-excursion
+                (goto-char s)
+                (search-forward "\\\\" p t)))
+           n)
+      (save-excursion
+        (goto-char s)
+        (setq n (how-many "[^\\]&" s e)))
+      (when n
+        (save-excursion
+          (insert (make-string n ?&)))))))
+
 (defvar LaTeX-amsmath-package-options '("intlimits" "nointlimits"
                                         "sumlimits" "nosumlimits"
                                         "namelimits" "nonamelimits"
--8<---------------cut here---------------end--------------->8---

Best, Arash