G713: correct gamma density at zero

crates/functions/src/stat/distributions.rs

@@ -499,7 +499,7 @@ pub(super) fn gamma_dist(a: &[Arg], _: C) -> R<Value> {
         return if al < 1.0 {
             Err(CellError::Num)
         } else if al == 1.0 {
-            num_val(1.0 / be)
+            Err(CellError::Num)
         } else {
             num_val(0.0)
         };

crates/functions/src/stat/tests.rs

@@ -479,6 +479,19 @@ fn continuous() {
     close_tol(r[0][1].clone(), 0.841344746, 1e-8);
 }
 
+#[test]
+fn gamma_density_at_zero_shape_one_is_num() {
+    for scale in [0.1, 0.9, 1.0, 1.9, 2.0, 10_000_000_000.0] {
+        is_err(ev("GAMMA.DIST", vec![n(0.0), n(1.0), n(scale), b(false)]), CellError::Num);
+    }
+    is_err(ev("GAMMA.DIST", vec![n(0.0), n(0.5), n(1.0), b(false)]), CellError::Num);
+    close_tol(ev("GAMMA.DIST", vec![n(0.0), n(2.0), n(1.0), b(false)]), 0.0, 0.0);
+    close_tol(ev("GAMMA.DIST", vec![n(0.0), n(1.0), n(2.0), b(true)]), 0.0, 0.0);
+    close_tol(ev("GAMMA.DIST", vec![n(2.0), n(1.0), n(2.0), b(false)]), 0.5 * (-1.0f64).exp(), 1e-15);
+    close_tol(ev("GAMMA.DIST", vec![n(2.0), n(1.0), n(2.0), b(true)]), 1.0 - (-1.0f64).exp(), 1e-15);
+    is_err(ev("GAMMA.DIST", vec![n(-0.1), n(1.0), n(2.0), b(false)]), CellError::Num);
+}
+
 #[test]
 fn aggregate_helper() {
     let vals = vec![nv(1.0), nv(2.0), tv("x"), Value::Empty, Value::Bool(true), nv(6.0)];

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-25 · **Change:** minor (the LAMBDA row lists the recursion limit and its `#NUM!`, and the error a defined name holding an error gives when called; earlier: number text with accounting parentheses coerces like Excel 365; INDEX with one index on a 2-D reference is #REF! as in Excel; earlier: SUBTOTAL and AGGREGATE cap the cells they visit, #2175) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (GAMMA.DIST density at x=0 and shape 1 returns `#NUM!` as in Excel; earlier: the LAMBDA row lists the recursion limit and its `#NUM!`, and the error a defined name holding an error gives when called; earlier: number text with accounting parentheses coerces like Excel 365; INDEX with one index on a 2-D reference is #REF! as in Excel; earlier: SUBTOTAL and AGGREGATE cap the cells they visit, #2175) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Excel's worksheet functions, category by category, against GridCraft's function library. Part of
 [target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
@@ -123,6 +123,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-31 | minor | GAMMA.DIST density at x=0 and shape 1 returns `#NUM!` for all positive scales; the cumulative branch and other shape boundaries are unchanged |
 | 2026-10-25 | minor | LAMBDA row: a LAMBDA that calls itself more than 140 times, and a formula nested past the depth limit, give `#NUM!` (#1809; nesting gave `#CALC!` before). `=Foo(1)` where the defined name Foo holds `#N/A` gives `#N/A`, not `#NAME?` |
 | 2026-10-23 | minor | Number text coercion (VALUE, arithmetic, typed entry): a dollar sign before accounting parentheses (`$(1,234)`, `$ (5)`) and a percent sign after them (`(5)%`) read as negatives; `(-5)`, `((5))`, `($-5)`, `$5%`, `$(5)%` and dates or times in parentheses are `#VALUE!`, as observed in Excel 365 |
 | 2026-10-23 | minor | INDEX with only a row index on a reference of several rows and columns (`INDEX(A1:C3,2)`, `INDEX(A1:C3,0)`) is `#REF!`, as observed in Excel, so it also fails as a range endpoint and inside other functions; an empty column argument (`INDEX(A1:C3,2,)`) still gives the row. Checked that a column array with one index stays a 1×1 array (`TYPE` 64), which is what Excel returns |