Disregard my earlier concerns. I found my error: the input vector from the gsl code has 1s in the first 11 positions, not the first 10 positions. Now all 3 implementations agree. Jim -- James W. Haefner Department of Biology Email: jhaefner@biology.usu.edu Utah State University Voice: 435-797-3553 Logan, UT 84322-5305 Fax: 435-797-1575