**The MAIN MENU links the four subsidiary menus together, and is called
from any other menu by the Escape key. The Options are:**

**N** **Number of Pixels**

An even number (2 <= N <= N_{max},
default N = 256) is selectable, either by indicated code letter
or by the numerical value. If N is changed, all arrays are cleared. The
maximum number is determined by the computer configuration; typically N_{max }= 8192.

**I Index Range
of Arrays **

The selection is a toggle -- either [-N/2, N/2 - 1] or [0, N-1). The values in the array are not disturbed.

**Z** **Zeros (Initializes)
both Arrays**

Set amplitudes of all samples in both arrays to zero.

**X** ** Exit to DOS
Shell**

Type "exit" to return to *SIGNALS*.

**M** **Set FFT and
DFT Normalization **

The choices scale the amplitudes computed in the forward transform by 1/N, 1, or SQR(1/N) (default); the corresponding factors in the inverse transform are 1, 1/N, and SQR(1/N). The normalizations ensure that a cascade of the forward and inverse FFT produce the original array amplitudes.

**L** **Load data array
from disk**

The ASCII format saves arrays with a file extension ".DAT" as a column of 2N + 1 elements: the first is the number of pixels N, followed by the N real samples and N imaginary samples of the data array.

**S** **Save data in
spreadsheet format **

This ASCII format with file extension ".SSF" (for ** S**pread

**<ESC>ape key** **Quit
SIGNALS**

**F** **FUNCTION Menu
**

**O** **OPERATIONS Menu**

**A** **ARITHMETIC Menu**

**P** **PLOT Menu **

RETURN to OVERVIEW of SIGNALS MANUAL

OPTIONS in MAIN MENU

OPTIONS in FUNCTIONS MENU

OPTIONS in OPERATIONS MENU

OPTIONS in ARITHMETIC MENU

OPTIONS in PLOT MENU