You may be aware that "Fortran" is a contraction of "formula translator." It should then come as no surprise that the Fortran language includes a full complement of mathematical operations in addition to the basic arithmetic operations of addition, subtraction, multiplication and division.
One such operation is exponentiation, which is indicated by the double asterisk ** as in the following example:
A = B ** 3
Here the variable A is being assigned a value that is equal to the cube of another variable, B.
Fractional powers may be used: for example, if we want to take the fourth root of some variable C, we could write this as:
D = C ** 0.25
The following operators take the form of functions. A function operates on one or more inputs, called arguments, that are placed in parentheses after the function. Some of the most commonly used mathematical functions are as follows:
| Function | Meaning |
Y = EXP (X) |
Exponential of the argument X; that is, the variable e to the power X. |
Y = ALOG (X) |
Natural logarithm of the argument X. Attempting to take the logarithm of a negative number will cause the system to report an error. |
Y = SIN (X) |
Sine of the argument X. Important: X is expressed in radians. |
Y = COS (X) |
Cosine of the argument X. Important: X is expressed in radians. |
Y = TAN (X) |
Tangent of the argument X. Important: X is expressed in radians. |
Y = ASIN (X) |
Arcsine of the argument X. The result will be in radians, with a value between -pi and +pi. |
Y = ACOS (X) |
Arccosine of the argument X. The result will be in radians, with a value between -pi and +pi. |
Y = ATAN (X) |
Single-argument arctangent. Here Y is the arctangent of the argument X. The result will be in radians, with a value between -pi/2 and +pi/2. |
Y = ATAN2 (X, Z) |
Two-argument arctangent; the result is the arctangent of X/Z, in radians. The use of two arguments allows the determination of the quadrant of the angle, so that the result is between -pi and +pi rather than -pi/2 and +pi/2. |
Assignment: Write a brief program to compute the solar elevation angle following the instructions for Homework 3. Write the program so that the answer is reported in both degrees and radians.