if (trigger.isUpdate) {
         integer  i = 0;
         list<AccountOne__c> a2 = new list<AccountOne__c>([SELECT Id 
                                                           FROM AccountOne__c 
                                                           WHERE Name = trigger.old[i].Name]);
         for (AccountOne__c c1 : a2) {    
             c1.Name = trigger.new[i].name;
             c1.Fax__C = trigger.new[i].Fax;
             c1.Phone__C = trigger.new[i].Phone;
             i++;
         }
         update a2;
     }


 


----------


     if (trigger.isUpdate) {
         integer  i = 0;
         list<AccountOne__c> a2 = new list<AccountOne__c>([SELECT Id 
                                                           FROM AccountOne__c 
                                                           WHERE Name =: trigger.old[i].Name ]);
         for (AccountOne__c c1 : a2) {
             c1.Name = trigger.new[i].name;
             c1.Fax__C = trigger.new[i].Fax;
             c1.Phone__C = trigger.new[i].Phone;
             i++;
         }
         update a2;
     }

i tried bulk trigger for the update operation ,but its not working can anyone help me