lire les messages de ce fil de discussion, cela parle des fonctions d'approximations
<http://groups.google.fr/groups?hl=fr&lr=&ie=UTF-8&oe=UTF-8&threadm=ejRUy6QCDHA.392%40TK2MSFTNGP12.phx.gbl&rnum=1&prev=/groups%3Fq%3Dgroup:*fr.excel%2Baire%2Bsous%2Bcourbe%26hl%3Dfr%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26scoring%3Dd>