196 Section 14: Numerical Integration

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0 v

0.0000

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3.1416

R

3.1416

Run mode.

Key lower limit, 0, into Y- register.

Key upper limit, π, into X- register.

Specify Radians mode for trigonometric functions.

Now you are ready to press ´f 0 to calculate the integral. When you do so, you'll find that – just as with _– the calculator will not display the result right away, as it does with other operations. The HP-15C calculates integrals using a sophisticated iterative algorithm. Briefly, this algorithm evaluates f(x), the function to be integrated, at many values of x between the limits of integration. At each of these values, the calculator evaluates the function by executing the subroutine you write for that purpose. When the calculator must execute the subroutine many times – as it does when you press f– you can't expect any answer right away. Most integrals will require on the order of 2 to 10 seconds; but some integrals will require even more. Later on we'll discuss how you can decrease the time somewhat; but for now press ´f 0 and take a break (or read ahead) while the HP-15C takes care of the drudgery for you.

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´f0

2.4040

= ∫π cos (sinθ) dθ .

 

 

0

In general, don't forget to multiply the value of the integral by whatever constants, if any, are outside the integral. In this particular problem, we need to multiply the integral by 1/ π to get J0 (1):

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0.7652

J0 (1).