, montre que ||G|| ? < ? si et seulement si H(?) n'a pas de valeur propre sur l'axe imaginaire. L'algorithme suivant permet alors d'approximer la norme H ? de G : 1. Choisir un intervalle grossier

, Calculer le spectre de H(?) pour ? = 1 2 (? min + ? max )

, Si H(?) n'a pas de valeurs propres sur l'axe imaginaire, alors ? est trop grand. On peut alors raffiner l'intervalle en revenant à l'étape 1 et avec le nouveau encadrement

, Sinon, ? est trop petit et on peut raffiner l'intervalle en revenant à l'étape 1 et avec l'encadrement

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