Section 4: Statistics Functions

57

Keystrokes

Display

 

 

70 ´j

7.56

Predicted grain yield in tons/hectare.

 

®

0.99

The original data closely approximates a

 

 

straight line.

 

Other Applications

Interpolation. Linear interpolation of tabular values, such as in thermodynamics and statistics tables, can be carried out very simply on the HP-15C by using the j function. This is because linear interpolation is linear estimation: two consecutive tabular values are assumed to form two points on a line, and the unknown intermediate value is assumed to fall on that same line.

Vector Arithmetic. The statistical accumulation functions can be used to perform vector addition and subtraction. Polar vector coordinates must be converted to rectangular coordinates upon entry (θ, v, r ;, z). The results are recalled from R3 (Σx) and R5 (Σy) (using l z) and converted back to polar coordinates, if necessary. Remember that for polar coordinates the angle is between -180° and 180° (or and π radians, or - 200 and 200 grads). To convert to a positive angle, add 360 (or 2π or 400) to the angle.

For the second vector entered, the final keystroke will be either z or w, depending on whether the two vectors should be added or subtracted.