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Commit 4daba4b

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zhunago

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log sum exp trick

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algorithm
- numstab.cpp

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`‎algorithm/numstab.cpp‎`

Lines changed: 36 additions & 0 deletions

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	`1`	`+#include <iostream>`
	`2`	`+using namespace std;`
	`3`	`+`
	`4`	`+void overflow()`
	`5`	`+{`
	`6`	`+ double a = exp(998);`
	`7`	`+ double b = exp(1000);`
	`8`	`+`
	`9`	`+ double c = 0;`
	`10`	`+ for(int i = 0; i < 100; ++i)`
	`11`	`+ {`
	`12`	`+ c += exp(-2);`
	`13`	`+ }`
	`14`	`+ cout << 1000 + log(c + 1) << endl;`
	`15`	`+ cout << log(b + a *100) << endl;`
	`16`	`+}`
	`17`	`+`
	`18`	`+void underflow()`
	`19`	`+{`
	`20`	`+ double a = exp(-1000);`
	`21`	`+ double b = exp(-999);`
	`22`	`+`
	`23`	`+ double c = 0;`
	`24`	`+ for(int i = 0; i < 100; ++i)`
	`25`	`+ {`
	`26`	`+ c += exp(-1);`
	`27`	`+ }`
	`28`	`+ cout << -999 + log(c + 1) << endl;`
	`29`	`+ cout << log(b + a *100) << endl;`
	`30`	`+}`
	`31`	`+int main(void)`
	`32`	`+{`
	`33`	`+ overflow();`
	`34`	`+ underflow();`
	`35`	`+ return 0;`
	`36`	`+}`

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