expIntegralEi around origin

paulmasson · Apr 7, 2022 · a049049 · a049049
1 parent 8ecb6f1
commit a049049
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git a/build/math.js b/build/math.js
@@ -2229,7 +2229,9 @@ function expIntegralEi( x, adjustImForGamma=false, tolerance=1e-10 ) {
     var distanceScale = abs( sub(x,useAsymptotic) ) / useAsymptotic;
     var useArbitrary = distanceScale > 1;
 
-    if ( useArbitrary ) {
+    // arbitrary precision series is unstable around the origin but not needed
+
+    if ( useArbitrary && abs(x) > 1.5 ) {
 
       // use only decimals needed
       var n = 17 + Math.round( 10 * ( distanceScale - 1 ) );

diff --git a/src/functions/gamma.js b/src/functions/gamma.js
@@ -481,7 +481,9 @@ function expIntegralEi( x, adjustImForGamma=false, tolerance=1e-10 ) {
     var distanceScale = abs( sub(x,useAsymptotic) ) / useAsymptotic;
     var useArbitrary = distanceScale > 1;
 
-    if ( useArbitrary ) {
+    // arbitrary precision series is unstable around the origin but not needed
+
+    if ( useArbitrary && abs(x) > 1.5 ) {
 
       // use only decimals needed
       var n = 17 + Math.round( 10 * ( distanceScale - 1 ) );