Where is this method called - (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
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Im just starting to look at Open GL ES for iOS and I'm looking through the source code on apples template code. The problem is both 

`- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect` 

and 

`- (void)update` 

are being called, but I'm unable to determine by what and how to change the frequency?