space group formatting: add overline for negative numbers

lib/utils/formatting.jsx

@@ -8,16 +8,48 @@ export function formatChemicalFormula(formula) {
     return v;
   });
 }
+const overlineStyle = {
+  display: "inline-block",
+  position: "relative",
+};
+
+const overlineAdjustmentStyle = {
+  position: "absolute",
+  top: "0.15em",
+  left: 0,
+  right: 0,
+  borderTop: "0.1em solid black",
+  height: 0,
+  zIndex: 1,
+};
 
 export function formatSpaceGroupSymbol(params) {
+  /*
+   * Note: there is no case where both subscript and overline need
+   * to be applied to the same number.
+   */
   let nextIsSub = false;
+  let nextIsNegative = false;
   return (
     <span>
       {params.split("").map((v, index) => {
+        if (v == "-") {
+          nextIsNegative = true;
+          return null;
+        }
         if (v == "_") {
           nextIsSub = true;
           return null;
         }
+        if (nextIsNegative) {
+          nextIsNegative = false;
+          return (
+            <span style={overlineStyle} key={index}>
+              <span style={overlineAdjustmentStyle} />
+              {v}
+            </span>
+          );
+        }
         if (nextIsSub) {
           nextIsSub = false;
           return <sub key={index}>{v}</sub>;

lib/utils/symmetry.js

@@ -7,6 +7,7 @@
  * - https://github.com/spglib/spglib/blob/v2.5.0/database/make_spgtype_db.py
  * - https://github.com/materialsproject/pymatgen/blob/v2024.8.9/src/pymatgen/symmetry/analyzer.py
  * - https://raw.githubusercontent.com/materialsproject/pymatgen/v2024.8.9/src/pymatgen/symmetry/symm_ops.json
+ * - https://aflow.org/prototype-encyclopedia/spacegroup_info.html
  */
 
 // Import the international (Hermann-Mauguin) space and point group symbols
@@ -23,6 +24,8 @@ const PEARSON_CRYSTAL_FAMILIES = {
   h: "hexagonal",
   c: "cubic",
 };
+// Note that for "base-centered" other sources might use a different letter
+// (e.g. 'C' instead of 'S')
 const PEARSON_BRAVAIS_LATTICES = {
   aP: "triclinic",
   mP: "simple monoclinic",

src/App.jsx

@@ -82,6 +82,7 @@ function App() {
       <span>utils/formatting.jsx</span>
       <div>{formatChemicalFormula("CO2")}</div>
       <div>{formatSpaceGroupSymbol("P6_3/mcm")}</div>
+      <div>{formatSpaceGroupSymbol("P-42_1m")}</div>
       <span>utils/symmetry.js</span>
       <div>
         <Table bordered striped>