fix gamma_inc max precision (#210)

Author: birm

src/gamma_inc.jl

@@ -567,7 +567,7 @@ function gamma_inc_minimax(a::Float64, x::Float64, z::Float64)
         c5 = @horner(z , d50 , d5[1])
         c6 = @horner(z , d60 , d6[1])
 
-        t = @horner(u , c0 , c1 , c2 , c3 , c4 , c5 , c6 , d70 , d80)
+        t = @horner(z , c0 , c1 , c2 , c3 , c4 , c5 , c6 , d70 , d80)
         if l < 1.0
             p = c*(w - rt2pin*t/sqrt(a))
             return (p , 1.0 - p)

test/gamma_inc.jl

@@ -34,6 +34,8 @@
     @test gamma_inc(0.9,0.8,0)[1] ≈ 0.59832030278768172
     @test gamma_inc(1.7,2.5,0)[1] ≈ 0.78446115627678957
     @test gamma_inc(11.1,0.001,0)[2] ≈ 1.0000
+    @test gamma_inc(1e7, (1e7)+1, 0)[1] ≈ 0.5001682088254367
+    @test gamma_inc(1e7, (1e7)+1, 0)[2] ≈ 0.4998317911745633
     @test_throws DomainError gamma_inc(-1,2,2)
     @test_throws DomainError gamma_inc(0,0,1)
 end