how to make a sumation using f(x) where x>a

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how to make a sumation using f(x) where x>a

Postby batmanmg » Sat Apr 25, 2009 4:55 am

ok, im stumped. i've been running through my calculators manual like crazy, and then tried to rethink the situation and make the functions terms confine it to that range instead of artificially instating the greater than limitation.


in other words. if i have sin(4x), sin(8x), sin(12x)....sin(n4x)
but only want to use the sin(4x) for x>1, and only the sin(8x) for x>2, the sin(12x) for x>3...
when creating the sumation to describe

∑ sin(i4x) for x>i

now the tricky part, is that i'd like to check the accuracy on my calculator for small n, but i don't have any way to define a function with a x> without getting a nice little, error, argument must be an expression. does anyone know any math tricks that could help me out with this one?
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Re: how to make a sumation using f(x) where x>a

Postby Keiji » Tue Apr 28, 2009 9:27 am

Most calculators would implement true as 1 and false as 0 if they even supported logical operators, so you could write ∑sin(i4x)*(x>i).
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Re: how to make a sumation using f(x) where x>a

Postby batmanmg » Wed Sep 08, 2010 10:59 pm

well that was rude of my former self. thank you Keiji
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