Support {smallmatrix}, {subarray}, and \substack (#1969)

* Support {smallmatrix}, {subarray}, and \substack

* Fix lint errors

* Update docs. Screenshots step 1.

* Screenshots step 2

* Screenshots step 3

* Pick up review comments

* Fixed arraycolsep for {smallmatrix}

* Fixed lint error

* Updated screenshots

docs/support_table.md

@@ -928,7 +928,7 @@ table td {
 |\small|$\small small$|`\small small`|
 |\smallfrown|$\smallfrown$||
 |\smallint|$\smallint$||
-|{smallmatrix}|<span style="color:firebrick;">Not supported</span>||
+|{smallmatrix}|$\begin{smallmatrix} a & b \\ c & d \end{smallmatrix}$|`\begin{smallmatrix}`<br>&nbsp;&nbsp;&nbsp;`a & b \\`<br>&nbsp;&nbsp;&nbsp;`c & d`<br>`\end{smallmatrix}`|
 |\smallsetminus|$\smallsetminus$||
 |\smallsmile|$\smallsmile$||
 |\smash|$\left(x^{\smash{2}}\right)$|`\left(x^{\smash{2}}\right)`|
@@ -965,7 +965,7 @@ table td {
 |\subseteqq|$\subseteqq$||
 |\subsetneq|$\subsetneq$||
 |\subsetneqq|$\subsetneqq$||
-|\substack|<span style="color:firebrick;">Not supported</span>||
+|\substack|$$\sum_{\substack{0<i<m\\0<j<n}}$$|`\sum_{\substack{0<i<m\\0<j<n}}`|
 |\succ|$\succ$||
 |\succapprox|$\succapprox$||
 |\succcurlyeq|$\succcurlyeq$||

docs/supported.md

@@ -85,6 +85,7 @@ $( \big( \Big( \bigg( \Bigg($ `( \big( \Big( \bigg( \Bigg(`
 |$\begin{Bmatrix} a & b \\ c & d \end{Bmatrix}$ |`\begin{Bmatrix}`<br>&nbsp;&nbsp;&nbsp;`a & b \\`<br>&nbsp;&nbsp;&nbsp;`c & d`<br>`\end{Bmatrix}`|$\def\arraystretch{1.5}\begin{array}{c:c:c} a & b & c \\ \hline d & e & f \\ \hdashline g & h & i \end{array}$|`\def\arraystretch{1.5}`<br>&nbsp;&nbsp;&nbsp;`\begin{array}{c:c:c}`<br>&nbsp;&nbsp;&nbsp;`a & b & c \\ \hline`<br>&nbsp;&nbsp;&nbsp;`d & e & f \\`<br>&nbsp;&nbsp;&nbsp;`\hdashline`<br>&nbsp;&nbsp;&nbsp;`g & h & i`<br>`\end{array}`
 |$\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}$ |`\begin{aligned}`<br>&nbsp;&nbsp;&nbsp;`a&=b+c \\`<br>&nbsp;&nbsp;&nbsp;`d+e&=f`<br>`\end{aligned}`|$\begin{alignedat}{2}10&x+&3&y=2\\3&x+&13&y=4\end{alignedat}$ |`\begin{alignedat}{2}`<br>&nbsp;&nbsp;&nbsp;`10&x+ &3&y = 2 \\`<br>&nbsp;&nbsp;&nbsp;` 3&x+&13&y = 4`<br>`\end{alignedat}`
 |$\begin{gathered} a=b \\ e=b+c \end{gathered}$ |`\begin{gathered}`<br>&nbsp;&nbsp;&nbsp;`a=b \\ `<br>&nbsp;&nbsp;&nbsp;`e=b+c`<br>`\end{gathered}`|$x = \begin{cases} a &\text{if } b \\ c &\text{if } d \end{cases}$ |`x = \begin{cases}`<br>&nbsp;&nbsp;&nbsp;`a &\text{if } b  \\`<br>&nbsp;&nbsp;&nbsp;`c &\text{if } d`<br>`\end{cases}`
+|$\begin{smallmatrix} a & b \\ c & d \end{smallmatrix}$ | `\begin{smallmatrix}`<br>&nbsp;&nbsp;&nbsp;`a & b \\`<br>&nbsp;&nbsp;&nbsp;`c & d`<br>`\end{smallmatrix}` | | |
 
 </div>
 
@@ -205,7 +206,7 @@ In display math, KaTeX does not insert automatic line breaks. It ignores display
 |:--------------|:----------------------------------------|:-----
 |$x_n$ `x_n` |$\stackrel{!}{=}$ `\stackrel{!}{=}`  |$a \atop b$ `a \atop b`
 |$e^x$ `e^x` |$\overset{!}{=}$ `\overset{!}{=}` |$a\raisebox{0.25em}{b}c$ `a\raisebox{0.25em}{b}c`
-|$_u^o $ `_u^o `|$\underset{!}{=}$ `\underset{!}{=}`
+|$_u^o $ `_u^o `|$\underset{!}{=}$ `\underset{!}{=}` | $$\sum_{\substack{0<i<m\\0<j<n}}$$ `\sum_{\substack{0<i<m\\0<j<n}}`
 
 The second argument of `\raisebox` can contain math if it is nested within `$…$` delimiters, as in `\raisebox{0.25em}{$\frac a b$}`
 

src/environments/array.js

@@ -1,5 +1,6 @@
 // @flow
 import buildCommon from "../buildCommon";
+import Style from "../Style";
 import defineEnvironment from "../defineEnvironment";
 import defineFunction from "../defineFunction";
 import mathMLTree from "../mathMLTree";
@@ -26,7 +27,7 @@ export type AlignSpec = { type: "separator", separator: string } | {
 };
 
 // Type to indicate column separation in MathML
-export type ColSeparationType = "align" | "alignat";
+export type ColSeparationType = "align" | "alignat" | "small";
 
 function getHLines(parser: Parser): boolean[] {
     // Return an array. The array length = number of hlines.
@@ -175,7 +176,16 @@ const htmlBuilder: HtmlBuilder<"array"> = function(group, options) {
 
     // Horizontal spacing
     const pt = 1 / options.fontMetrics().ptPerEm;
-    const arraycolsep = 5 * pt; // \arraycolsep in article.cls
+    let arraycolsep = 5 * pt; // default value, i.e. \arraycolsep in article.cls
+    if (group.colSeparationType && group.colSeparationType === "small") {
+        // We're in a {smallmatrix}. Default column space is \thickspace,
+        // i.e. 5/18em = 0.2778em, per amsmath.dtx for {smallmatrix}.
+        // But that needs adjustment because LaTeX applies \scriptstyle to the
+        // entire array, including the colspace, but this function applies
+        // \scriptstyle only inside each element.
+        const localMultiplier = options.havingStyle(Style.SCRIPT).sizeMultiplier;
+        arraycolsep = 0.2778 * (localMultiplier / options.sizeMultiplier);
+    }
 
     // Vertical spacing
     const baselineskip = 12 * pt; // see size10.clo
@@ -379,7 +389,7 @@ const alignMap = {
 };
 
 const mathmlBuilder: MathMLBuilder<"array"> = function(group, options) {
-    const table = new mathMLTree.MathNode(
+    let table = new mathMLTree.MathNode(
         "mtable", group.body.map(function(row) {
             return new mathMLTree.MathNode(
                 "mtr", row.map(function(cell) {
@@ -401,7 +411,9 @@ const mathmlBuilder: MathMLBuilder<"array"> = function(group, options) {
 
     // The 0.16 and 0.09 values are found emprically. They produce an array
     // similar to LaTeX and in which content does not interfere with \hines.
-    const gap = 0.16 + group.arraystretch - 1 + (group.addJot ? 0.09 : 0);
+    const gap = (group.arraystretch === 0.5)
+        ? 0.1  // {smallmatrix}, {subarray}
+        : 0.16 + group.arraystretch - 1 + (group.addJot ? 0.09 : 0);
     table.setAttribute("rowspacing", gap + "em");
 
     // MathML table lines go only between cells.
@@ -463,6 +475,8 @@ const mathmlBuilder: MathMLBuilder<"array"> = function(group, options) {
         table.setAttribute("columnspacing", spacing.trim());
     } else if (group.colSeparationType === "alignat") {
         table.setAttribute("columnspacing", "0em");
+    } else if (group.colSeparationType === "small") {
+        table.setAttribute("columnspacing", "0.2778em");
     } else {
         table.setAttribute("columnspacing", "1em");
     }
@@ -484,13 +498,18 @@ const mathmlBuilder: MathMLBuilder<"array"> = function(group, options) {
         table.setAttribute("rowlines", rowLines.trim());
     }
 
-    if (menclose === "") {
-        return table;
-    } else {
-        const wrapper =  new mathMLTree.MathNode("menclose", [table]);
-        wrapper.setAttribute("notation", menclose.trim());
-        return wrapper;
+    if (menclose !== "") {
+        table = new mathMLTree.MathNode("menclose", [table]);
+        table.setAttribute("notation", menclose.trim());
     }
+
+    if (group.arraystretch && group.arraystretch < 1) {
+        // A small array. Wrap in scriptstyle so row gap is not too large.
+        table = new mathMLTree.MathNode("mstyle", [table]);
+        table.setAttribute("scriptlevel", "1");
+    }
+
+    return table;
 };
 
 // Convenience function for aligned and alignedat environments.
@@ -656,6 +675,63 @@ defineEnvironment({
     mathmlBuilder,
 });
 
+defineEnvironment({
+    type: "array",
+    names: ["smallmatrix"],
+    props: {
+        numArgs: 0,
+    },
+    handler(context) {
+        const payload = {arraystretch: 0.5};
+        const res = parseArray(context.parser, payload, "script");
+        res.colSeparationType = "small";
+        return res;
+    },
+    htmlBuilder,
+    mathmlBuilder,
+});
+
+defineEnvironment({
+    type: "array",
+    names: ["subarray"],
+    props: {
+        numArgs: 1,
+    },
+    handler(context, args) {
+        // Parsing of {subarray} is similar to {array}
+        const symNode = checkSymbolNodeType(args[0]);
+        const colalign: AnyParseNode[] =
+            symNode ? [args[0]] : assertNodeType(args[0], "ordgroup").body;
+        const cols = colalign.map(function(nde) {
+            const node = assertSymbolNodeType(nde);
+            const ca = node.text;
+            // {subarray} only recognizes "l" & "c"
+            if ("lc".indexOf(ca) !== -1) {
+                return {
+                    type: "align",
+                    align: ca,
+                };
+            }
+            throw new ParseError("Unknown column alignment: " + ca, nde);
+        });
+        if (cols.length > 1) {
+            throw new ParseError("{subarray} can contain only one column");
+        }
+        let res = {
+            cols,
+            hskipBeforeAndAfter: false,
+            arraystretch: 0.5,
+        };
+        res = parseArray(context.parser, res, "script");
+        if (res.body[0].length > 1) {
+            throw new ParseError("{subarray} can contain only one column");
+        }
+        return res;
+    },
+    htmlBuilder,
+    mathmlBuilder,
+});
+
 // A cases environment (in amsmath.sty) is almost equivalent to
 // \def\arraystretch{1.2}%
 // \left\{\begin{array}{@{}l@{\quad}l@{}} … \end{array}\right.

src/macros.js

@@ -426,6 +426,9 @@ defineMacro("\\varPhi", "\\mathit{\\Phi}");
 defineMacro("\\varPsi", "\\mathit{\\Psi}");
 defineMacro("\\varOmega", "\\mathit{\\Omega}");
 
+//\newcommand{\substack}[1]{\subarray{c}#1\endsubarray}
+defineMacro("\\substack", "\\begin{subarray}{c}#1\\end{subarray}");
+
 // \renewcommand{\colon}{\nobreak\mskip2mu\mathpunct{}\nonscript
 // \mkern-\thinmuskip{:}\mskip6muplus1mu\relax}
 defineMacro("\\colon", "\\nobreak\\mskip2mu\\mathpunct{}" +

test/katex-spec.js

@@ -2582,6 +2582,43 @@ describe("An array environment", function() {
 
 });
 
+describe("A subarray environment", function() {
+
+    it("should accept only a single alignment character", function() {
+        const parse = getParsed`\begin{subarray}{c}a \\ b\end{subarray}`;
+        expect(parse[0].type).toBe("array");
+        expect(parse[0].cols).toEqual([
+            {type: "align", align: "c"},
+        ]);
+        expect`\begin{subarray}{cc}a \\ b\end{subarray}`.not.toParse();
+        expect`\begin{subarray}{c}a & b \\ c & d\end{subarray}`.not.toParse();
+        expect`\begin{subarray}{c}a \\ b\end{subarray}`.toBuild();
+    });
+
+});
+
+describe("A substack function", function() {
+
+    it("should build", function() {
+        expect`\sum_{\substack{ 0<i<m \\ 0<j<n }}  P(i,j)`.toBuild();
+    });
+    it("should accommodate spaces in the argument", function() {
+        expect`\sum_{\substack{ 0<i<m \\ 0<j<n }}  P(i,j)`.toBuild();
+    });
+    it("should accommodate macros in the argument", function() {
+        expect`\sum_{\substack{ 0<i<\varPi \\ 0<j<\pi }}  P(i,j)`.toBuild();
+    });
+
+});
+
+describe("A smallmatrix environment", function() {
+
+    it("should build", function() {
+        expect`\begin{smallmatrix} a & b \\ c & d \end{smallmatrix}`.toBuild();
+    });
+
+});
+
 describe("A cases environment", function() {
 
     it("should parse its input", function() {

test/screenshotter/ss_data.yaml

@@ -37,7 +37,9 @@ Arrays: |
         1&2&3\\ \hline
         1+1&2+1&3+1\cr1\over2&\scriptstyle 1/2&\frac12\\[1ex] \hline \hdashline
         \begin{pmatrix}x\\y\end{pmatrix}&0&\begin{vmatrix}a&b\\c&d\end{vmatrix}
-    \end{array}\right]
+    \end{array}\right] \\
+    \begin{smallmatrix} a & b \\ c & d \end{smallmatrix} \;\;
+    \begin{subarray}{c}a \\ b\end{subarray}
 ArrayMode:
     tex: |
         \begin{matrix}
@@ -270,7 +272,8 @@ OpLimits: |
     \begin{matrix}
         {\sin_2^2 \lim_2^2 \int_2^2 \sum_2^2}
         {\displaystyle \lim_2^2 \int_2^2 \intop_2^2 \sum_2^2} \\
-        \limsup_{x \rightarrow \infty} x \stackrel{?}= \liminf_{x \rightarrow \infty} x
+        \limsup_{x \rightarrow \infty} x \stackrel{?}= \liminf_{x \rightarrow \infty} x \\
+        \displaystyle \sum_{\substack{0<i<m\\0<j<n}}
     \end{matrix}
 OverUnderline: x\underline{x}\underline{\underline{x}}\underline{x_{x_{x_x}}}\underline{x^{x^{x^x}}}\overline{x}\overline{x}\overline{x^{x^{x^x}}} \blue{\overline{\underline{x}}\underline{\overline{x}}}
 OverUnderset: |