# Examining the data

## Click open the Data Browser in order to use it. Typing (Esc) makes the main XPP window the "hot" window.

### The DATA BROWSER lets you examine and minipulate the numbers generated by your simulation. It also lets you import files of numbers for plotting . It acts like a very primitive spreadsheet.

Once you have computed a trajectory to an equation, you can use the Data Browser (here after, DB) to look at the data. There are some known ``bugs.'' You must sometimes grab it with the mouse and shake it to get the data to show up (no kidding!) Also, sometimes it will not resize properly; in this case, you must continue the integration to the current starting point (in other words, do nothing but press (C) and then (Enter).) To activate the DB, bring the window to the top and put the pointer inside the box.

Across the top is a menu of commands and then there follows a list of titles for the variables, time and the auxiliary functions. Using the arrow keys, the page keys, home and end keye or clicking on the appropriate commands allows you to scroll through the data. By resizing the DB you can get more or less data. Clicking on (Left) shifts the data window to the left and (Right) moves it to the right. The time column always stays fixed. If you do parametric or range calculations, the range variable is kept in the time column. (Home) takes you to the top of the data and (End) to the last row. The remaining commands will be described separately. The keyboard shortcuts to invoke them are in parentheses.

- (F)ind This pops up a window and asks for a variable and a value. It then looks through the data until it comes to the closest value to the specified that the variable takes. It only moves down the file so that you can find successive values by starting at the top. ( Hint: To find the largest or smallest value in a column, just set the value really high or really low; XPP will find the closest value.)
- (G)et This makes the top row of data the initial coonditions for a new integration.
- Re(p)lace This pops up a window asking you for a column to replace. Then it prompts you for a formula. Suppose you want to replace AUX1 with x+y-t where x,y are two variables. Then type AUX1 when asked which column to replace and then type in the formula and (OK). Each row in the requested column will be replaced by the values of your formula. Any valid XPP function or user-defined function can be used. Two special symbols can also be used when applied to single variables:

  Numerical integration and differentiation.

  - @VARIABLE replaces the column with the numerical derivative of the variable. You cannot use this within a formula, but once the column is replaced, it can be treated as any other column.
  - \&VARIABLE replaces the column with the numerical integral. Note that successive applications of the derivative and then the integral will result in the original plus a constant.
- (U)nreplace This undoes the most recent replacement.
- Fir(s)t This marks the top row in the DB (nothing is shown)as the start or first row for saving or restoring.
- Last (e) This marks the top row as the last or end row for saving or restoring. Using First and Last lets you mark and plot selected parts of your data.
- (T)able This lets you save data in a tabulated format that can then be used by XPP as a function or inputs. You must use the (First) and (Last) keys to mark the desired data you want to save. You are then prompted for the column name, the minimum and maximum you want your independent variable to range and the file name. The result is a table file of the format used by XPP.
- (R)estore replots the data marked by First and Last. The default is the entire data set

  Reading and writing numbers to files

- (W)rite prompts you for a filename and writes the marked data to a file. The files are of the form:

  t0 x1(t0) ... xn(t0)

  t1 x1(t0) ... xn(t0)

  .

  .

  .

  tf x1(tf) ... xn(tf)

  and reflect the current contents of the DB. They are ASCII readable. Thus you can use superior graphics programs to plot the results of your simulations.

- (L)oad Will load in as much of a similarly formated data file as possible for graphing.

  Adding and deleting columns of data

- (A)ddcol This allows you to add an additional column to the data browser. You are prompted for the name you want to give the column and for the formula. It is thus, like an auxiliary variable with a name. Thereafter, it will be computed along with any other quantities that you have defined. It is as though you had included another auxilliary variable in your original file.
- (D)elcol This lets you delete a column. You can only delete columns which you have created with the {\tt Addcol} command.

  Sometimes the names will not appear or go away on the browser. If you iconify it and then open it up again, they will appear as they should. Another problem that can occur is that you can delete a column that is itself referred to by a different column. This will result in wrong answers in the column. Thus, do not delete columns whose contents are used by other columns. Also, if you delete a column, its name is still known by the internal system but it has no real value. For these reasons, you should delete columns with caution. If the purpose of deleting them is to change the formula, use the right-hand-side editor, (File-Edit) instead. <\ul>

  # References

  ##
    Table of Contents
    Main Menu Items
    ODE Files and Examples
    Numerics Menu
    File Menu
    Freeze Menu
    AUTO Menu
    Data Browser
    I/O and Hardcopy
    XPP Basics
    Nonlinear ODEs
    Two-dimensions
    Three-dimensions and Beyond
    Phase Equations
    Chaos