Send us other useful equations you come up with and well publish another Solver article somewhere down the road.]
The Solver function is found in HP CALC on all three HP Palmtops. Solver lets you enter your own equations, with variables, into the Calculator, and solve for the different variables. An example will clarify this.
The Economic Order Quantity (EOQ) is an equation used by purchasing agents to calculate the optimum quantity of an item to order. It was shown in the HP 95LX Users Guide, but is missing from the 200LX Users Guide:
2*O*S
EOQ = SqRt of (-------)
C*P
It says the EOQ is the square root of 2 times the Ordering costs times the annual Sales, divided by the Carrying cost (as a percentage of inventory) times the Purchase price of a unit.
If you have a phenomenal memory you could key the formula in using just the single letters of the formula. However, Solver allows longer names to help remember what each variable is. For instance you can use OrderCost instead of O.
To enter the formula into Solver, Start HP Calc, press [MENU] Solve [F4] (Insert) on the 95LX or [CTRL] Solve [F2] (Insert) on the 100/200LX. Then key in:
EOQ=Sqrt(
2*OrderCost*AnnualSales/
( %CarryCost/100*PurchPrice
)
)
The formula could be keyed in all on one line. However, the indented style shows where the matching parentheses appear. Once you have the equation working properly, you can always edit the text and delete the extra spaces.
I usually like to add a line or two of comments about an equation: something that will jog my memory later on. Sometimes the best comment is a completed example:
!
EOQ = 860.21
OrderCost = 35.00
AnnualSales = 10,000.00
%CarryCost = 20.00
PurchPrice = 4.73
!
Note that anything between two exclamation points is ignored by Solver when it runs the equation.
When you press [F10] (OK) and [F9](Calc) to run the equation you will see the following screen:
HP Calc's Solver showing the Economic Order Quantity screen.
Notice that EOQ is associated with the F2 function key and the other variable names are associated with function keys F3 through F6. To solve for EOQ, key in 35 and press (F3); key in 10,000 (or 1E4) and press (F4); 20 and press (F5); 4.73 and press (F6). Finally press (F2) and the EOQ = 860.21 will appear on the Calc line.
You can also use the Up- and DownArrow to highlight any of the variable names on the display. Pressing (ENTER) will put the number from the Calc line into that variable. Pressing the space bar will solve for that variable.
Once you have a solution on the Calc line, you can press [CTRL]-[C] to copy the line to the clipboard and open Memo or Note-Takers Note field, and press [CTRL]-[V] to paste the line into a document. On the other hand, if you want to paste the number into Lotus 1-2-3, you'll need to start 1-2-3, return to HP Calcs Solver, press [N](STO) [Spacebar], switch to 1-2-3, move the cursor to where you want to put the number, and press [ENTER].
This article is a compilation of a number of Solver equations we found posted on the HPHAND forum of CompuServe. I've indicated the author at the beginning of each equation.
The equations below can be found in SOLVP23.EQN (found in SOLVP23.ZIP = ). You can load the .EQN file directly into Solver by first transferring it to your Palmtop, opening Solver, pressing (MENU) File Open and selecting SOLVP23 .EQN. (On the 95LX press (MENU) File Retrieve.)
SOLVP23.EQN contains all the equations in this article. If you spot one or more that you like, you can transfer them to another .EQN file using the following instructions:
[Note: SLVHLP.ZIP = is an updated version of HPSOLVE.PBK =, a handy database that answers many questions about Solver that can be used by all three Palmtops.]
Copying equations from Memo to Solver
You can key an equation directly into Solver as described above, or key it in to MEMO and use the Palmtops Clipboard feature to cut and paste it into Solver. The Solver .EQN file is nothing more than a text file with each separate equation having the following format:
{Name|!Comments! Equation}
{ -- The open French brace indicates the beginning of the Solver equation and is to the left of the Name you assign to the equation.
} -- The close French brace indicates the end of the equation and appears to the right of the last element in the equation.
Name| -- The Name of the equation comes first to the right of the open French brace { and is followed by the pipe symbol |.
!Comments! -- Comments are remarks that help you understand the equation, but have no effect on its operation. You don't have to enter any Comments or a Name for the equation to work, but they will help you remember months later what the equation is all about.
Comments are bracketed between exclamation marks !, and may appear anywhere between the pipe symbol | and the close French brace }.
Equation -- The actual Solver equation comes after the pipe symbol | and is followed by a close French brace }.
All the equations in this article are displayed as you would see them in an .EQN file, enclosed by French braces {}.
You can load the .EQN file into MEMO and use the Palmtops clip board feature to Cut and Paste these equations, or parts of an equation, from Memo into Solver. Do not copy the French braces into Solver. Follow these instructions:
You can also key in the equations manually, but do so very carefully, checking to see you have the correct number of parentheses. Don't type in the French braces {}. The Name field is to the left in the Solver Catalog listing, you don't need to type the pipe symbol |. If you make a mistake in keying in an equation (e.g., you don't put in the right number of parentheses) Solver will beep and display an error message. Solver automatically saves the equations you enter into the .EQN file you have open.
When you've finished keying in or pasting an equation, press (F10) (OK) ((ENTER) on the 95LX) and (F9) (Calc). Key in the variables and have fun.