Number 211a - Year End 2000

The Answer Man - Charting
by Bob Russell, Mar 2000, North Texas PC NEWS
We've weathered a number of crises with NTPCUG, and from each one we've come out with a wealth of teamwork and more experiences to talk about. Those shared experiences are among the fond memories I have accumulated during the years since we started back at SMU. The whole environment has changed since then, and we are looking for a home for the meeting place once again. Heraclitus told us in 800 BC that the nature of life is change, so we are carrying on an old tradition.     I've retired from Microsoft, so we have to come up with a new name for the column. "Tips and Tricks" is already taken. I scanned the Excel newsgroup yesterday, and it appears that there is a wealth of ideas there for a column that answers the questions people are asking. Let's try that for a beginning; since my real love is Excel, and many people are interested in that application, it seems natural to make that my centerpiece.     One question in the newsgroup that interested me was a charting question: "How can I plot y as a function of x?". That is written y=f(x). When we say that y is a function of x, what we mean is that for each value of x, there is a solution to the equation that relates y to that value of x. Depending on the degree of the equation, there may be multiple values of x that will produce y, but generally we are interested in the positive, real values that solve the equation.     In Excel, we refer to the function, or equation, as a formula. Formulas are written one to a cell in the Excel worksheet, and may be copied into succeeding cells for as many times as we have values to relate. The values of x are called independent values, and the values that result from the formulas that refer to the x values are the dependent values, called y values for short.	Let us take an example function, y=3x^2, read y equals 3 times x squared. In column A, I put my values of x, the independent variable, starting in cell A1 and going to A6. We can use 1,2,3,4,5,6 to begin with, and play with them later to see how the different values affect the line on the chart. In Cell B1, I type the function: =3*A1^2. This calculates the value of y that is the result of the value 1 for x. I use the drag and fill handle to copy the formula down to B2 through B6, and there are the results of the function for all the values of x in column A.     Now, insert a chart from the tool bar to invoke the chart wizard. Choose x,y scatter for the chart type, and make the range A1:B6. The line on the chart now gives us the value of y for each value of x that we reference. The fun part is that we can now change the values of x to whatever we like, and the values of y will change automatically to read the value of the function y=3*x^2. The curve we see on the chart is a parabola. This is the curve associated with the effect of gravity on a bullet or a cannon shell as it passes along its trajectory, where y is the height at any given point along the horizontal distance x, at regular intervals of x.     Please let me know whether this is the type of column I should write, or if you have questions that you would like to have answered. I will try to respond in future columns, or in email if the question is something you need right away.     [Editor's Note: Bob Russell is a long-time member of the NTPCUG, and was the original Membership Director back in the days when all the membership information was stored in a version of the ShareWare PCFile program.]
Number 211a - Year End 2000