update log1pexp log1mexp

PRML · Aug 26, 2017 · 159d5cd · 159d5cd
1 parent 272477e
commit 159d5cd
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Showing 2 changed files with 9 additions and 8 deletions.
diff --git a/common/log1mexp.m b/common/log1mexp.m
@@ -1,7 +1,7 @@
 function y = log1mexp(x)
-% Accurately compute y = log(1-exp(-x))
+% Accurately compute y = log(1-exp(x))
 % reference: Accurately Computing log(1-exp(-|a|)) Martin Machler
 y = x;
-i = x > log(2);
-y(i) = log1p(-exp(-x(i)));
-y(~i) = log(-expm1(-x(~i)));
+i = x < -log(2);
+y(i) = log1p(-exp(x(i)));
+y(~i) = log(-expm1(x(~i)));
diff --git a/common/log1pexp.m b/common/log1pexp.m
@@ -1,7 +1,8 @@
 function y = log1pexp(x)
 % Accurately compute y = log(1+exp(x))
-% reference: Accurately Computing log(1-exp(|a|)) Martin Machler
-seed = 33.3;
+% reference: Accurately Computing log(1-exp(-|a|)) Martin Machler
 y = x;
-idx = x<seed;
-y(idx) = log1p(exp(x(idx)));
+i = x > 18;
+j = i & (x <= 33.3);
+y(~i) = log1p(exp(x(~i)));
+y(j) = x(j)+exp(-x(j));