Excel Basics By Tom Peters & Laura Spielman

Transcription

1 Excel Basics By Tom Peters & Laura Spielman What is Excel? Microsoft Excel is a software program with spreadsheet format enabling the user to organize raw data, make tables and charts, graph and model such data in curves and trendlines for the purposes of extrapolation, interpolation and forecasting or prediction. It is used at Virginia Tech for both business and life science calculus courses. Getting Into Excel: To open Excel at the Emporium, begin on the Macintosh side of the computer. Go to the Launcher panel and click on Applications, then on Excel. You should see a window named Workbook 1. If you do not see that window, click and hold down File in the menu and go to New. Previewing your Printout: Under the View menu, go to Page Break Preview. This will automatically insert page breaks so you can properly align your work or adjust it as necessary. It is desirable to align data tables with their corresponding graphs on the same page if possible. Cells Data entries are contained in rectangular blocks called cells. Cells are identified with the letter of the column beginning with A Z and the number of the corresponding row. For example the very first cell is A1. Table of Values: a) To enter data on your spreadsheet, use the mouse to highlight the cell where you wish to start. Please enter your data in column form. After entering a value, you may use the arrow keys to move to other cells. b) To change the width of a column, highlight a cell in that column and then go to Format in the menu and click on Column, then Width. c) If you would like to change anything about the style of the cells (i.e. bold, italics, centering, etc.), click on the cell(s) to highlight them and use the toolbar that is above your spreadsheet to make changes. Edit-Fill-Series: This technique can be used to quickly create rows or columns of input for functions with any interval of length we choose. Note, this only works for data in a linear progression. Method I a) Select a cell and type in the value of the input variable at which you would like to begin (This will often be referred to as the start value.) Then hit the Return key. b) Now, highlight the cell by clicking on it. c) Then, in the menu, go to Edit, then Fill, then Series. In the upper-left corner, you will need to choose whether to enter your values in rows or columns. Please enter them in columns unless otherwise instructed in a lab.

2 Method II d) Next, enter a Step Value and a Stop Value. (The step value indicates the interval length you want to use and the stop value indicates the last value of the input variable you want to use.) Then hit the Return key. You ll notice a column of values going from your start value to the stop value with intervals of length step value. a) Enter the first 2 entries in column form. b) Highlight both entries by dragging the cursor with the mouse over them. c) Move the cursor over the right bottom corner until a black + is seen. d) Proceed to drag down the column until the desired value is obtained. e) Release and click outside the cell. Calculating Sums in Excel: There are 2 ways to add a column (or row) of values in Excel: 1) Just highlight the cells you wish to add along with one additional empty cell. Then, click on the summation button,, in the toolbar. The sum will appear in the empty cell. Or 2) In an empty cell, use the sum command in the form =sum(first:last) Such as =sum(x5:x25). Such a command would calculate the sum X5 + X6 + + X24 + X25 of the values in these cells. NOTE: If you need help remembering how to enter a function or command in Excel, use the Paste Function icon, f x, located on the toolbar. Calculating Function Values in Excel: The most important thing to note here is that Excel does not accept function definitions in terms of a variable, but instead, in terms of values in cells. NOTE: If you need help remembering how to enter a function or command in Excel, use the Paste Function icon, f x, located on the toolbar. Example: Suppose we have the following table of input values in Excel: A B 1 x f(x) Suppose also that we would like to compute the value of the function f(x) = x(3x 2 10) for each of these values. To do this, in cell B2, we would type =A2*(3*A2^2 10) (Include the equals sign) (This tells Excel to take the value in cell A2 and to evaluate it in f(x).)

3 Then, to apply this function to each of the input values in cells A3 through A6, move the cursor to the bottom right corner of cell B2 until a black cross sign appears and drag the cursor down to cell B6. Now you will have the value of the function for each of the x-values you chose. NOTE: It is very important when using Excel to 1) always type in the = sign 2) type in all arithmetic symbols you want to use. For instance, in the previous problem, neither of =A2(3*A2^2 10) or =A2*(3A2^2 10) would have worked. 3) when in doubt, add another set of parenthesis. Changing Cell Format: (Includes displaying a fixed number of decimals and changing column width) Highlight all cells you want to change. To highlight an entire row, click on the number label to the left. To highlight a column, click on the letter label on top. Under the Format menu, go to "Cells." Notice the choice of tabs used for adjusting cells. Under the "Number" tab there are lots of options. To change the number of decimals for a group of cells, go to "Number." On the right, you may type in the number of decimals you want displayed. Click on "OK" when you are finished making changes. To change the column width, go to Format and then Column. Choosing Width allows you to tell Excel the exact width you want the column to be. Choosing Auto Fit Selection will make the width of the chosen column slightly wider than the widest entry highlighted. This is generally a good choice. Putting Text in Excel: (Text Box) Here are instructions for how to type your answers on the Excel worksheet: Click on the Drawing icon in the tool bar. The icon contains a square, triangle, and circle. When you click on it, you activate another tool bar. It should appear in the bottom left hand corner of your screen. Choose the square with the letter A and some lines. Notice when you click on it the cursor changes shape.into a set of cross-hairs. Somewhere on your worksheet, hold down the mouse and drag to form a box. Put your text in it, change the size, and move it around the worksheet as needed. Plots: XY-Scatter Graph a) Highlight all the columns of data you wish to graph (excluding headings). b) Click on the ChartWizard. (The icon looks like a bar graph.) c) If you are using Excel 97 or 98, continue to part (d). (If you are using Excel 95 a black cross appears as the cursor. Click and drag the mouse to select a region where you wish your chart to be placed). d) The dialog box is now open. If you are in Excel 97 or 98, choose the xy-scatter graph. This type of graph is most common for this course. You may want to explore other types of graphs on your own. (Click on Next and continue if you are in Excel 95.) Then choose the type of xy-scatter graph you would like to view. Click on "Next" and continue. Note: In Excel 97 or 98 you will now have a plot with tabs "Data Range" and "Series." If you choose the xy-scatter plot, the first column will automatically be the domain. (In Excel 95, you are given choices for the number of data rows you wish to consider (e.g. connected by smoothed lines, etc). In order to express y as a function of x, use your mouse to change the column number to one and let row number be 0. This forces Excel to consider the x-values as the domain. Feel free to play with numbers to see what happens.)

4 e) Click on the Series tab. Notice that the data you have plotted is currently called "Series 1." You should change that by typing in a name for your data in the "Name" box. f) Click on Next and label the x-axis and the y-axis. You may now also title your graph. Now click on Finish and your graph will appear. If you wish to move your graph, single click on it and drag it wherever you want. To make other changes to your graph double click on the part of the graph you wish to change. An options box will appear. Producing Equations (Given a set of data): a) First, create a plot as explained above. Here, you should choose the xy-scatter graph and then choose the first chart sub-type with just the points not with connecting lines. (It will look neater this way.) b) Single click on any one of the data points in the plot. c) Click and hold down Chart in the menu and go to Add Trendline. (In Excel 95, go to Insert- Trendline) d) Now you can choose the type of equation that you wish to view over your data. After making your selection, if you have a bad fit, you may make changes. To make changes, highlight the trendline on your chart and go to Edit-Undo-Add Trendline. That trendline should be gone and you can try again. Highlight the data points again and click on Chart-Add Trendline (Insert-Trendline in Excel 95) to get the dialogue box. This time, make a different selection. e) Displaying the equation for the trendline on the graph: First, double click on the trendline. Under the Options menu, select Display Equation on Chart. (Note: You could have done this same thing when you were in the Chart-Add Trendline menu earlier.) (In Excel 95, click on Insert-Trendline-Options and then Display Equation on Chart.) Matrices and Excel A matrix is a rectangular array of numbers. Rows are horizontal and columns are vertical. Matrix Addition A = B= a) To perform any operation using matrices in excel, you must always highlight the number of cells needed for the answer first. b) Type = (B1:C2) + (B4:C5) c) You must hold down the control + shift and then hit enter.this key combination tells Excel to compute all the entries in the matrix. If you just press enter, then Excel will compute only the first entry.

5 d) Answer: A= B= A + B = Scalar Multiplication : You can multiply any matrix by a scalar by using the formula, = scalar * (first entry: last entry) of the matrix such as =3* (B2:C3). Example: A = A = Multiplication of Two Matrices: Recall that two matrices must have the same number of columns in the multiplicand as rows in the multiplier for multiplication to be defined. For example the product of an (mxn) and a (nxp)is a (mxp). a) You will need to highlight the correct number of rows and columns for the product. b) Use the mmult command for matrix multiplication. c) Type = mmult (matrix 1 first entry: matrix 1 last entry, matrix 2 first entry :matrix 2 last entry) d) Don t forget to hold down shift + control then enter. Example A= B = 2 3 AB =

6 Matrix Inverse: To solve systems of equations you will need to find the inverse of a matrix. Recall that not all matrices are invertible. a) Highlight the area for the answer as the inverse will have the same dimensions as the original matrix. b)use the command minverse c)type = minverse (first entry : last entry) d) Hold control + shift then enter. Example A= A-1=

7

8