**TI-84 Plus (and General Graphing): Semi Log Plots (LINLOG)**

**Introduction**

Many
applications, such as the Bode Plot, are plotted as a semi-log plot. In particular, a lin log plot is used. In a
lin log plot, the x-axis is on a logarithmic scale, while the y-axis is a
linear scale.

Graphing
calculators do not have a lin log plot mode (at least not that I know of). However, we can simulate lin log plots.

**How to Simulate Lin Log Plots**

We are going to
enter Function plotting mode (y(x)) as usual.
The trick here is to substitute every x with 10^x or ALOG(x). For example:

y(x) = 5*x – 2 becomes

y(x)
= 5 *

**10^x**– 2 or y(x) = 5 ***ALOG(x)**– 2
In essence, we
think of the x axis not as {0, 1, 2, 3, …} but {10^0, 10^1, 10^2, 10^3, ….
}.

Caution: With certain functions, the range can grow
quickly. Be careful on how you set the
axis.

Reference: 10^0 = 1, 10^1 = 10, 10^2 = 100, 10^3 = 1,000

The TI-84 Plus
program LINLOG uses a list plot of a function and sets the axis to the
appropriate settings.

**TI-84 Plus Program LINLOG**

PlotsOff

FnOff

Disp
"LOGARITHMIC X AXIS"

Disp
"10^{0,1,2,...,N}"

Disp "USE
QUOTES"

Input "Y =
",Y₁

Input "TO 10^N:
",N

{0}→L1

10^(0)→X

{Y1}→L2

For(I,0,N,0.1)

10^(I)→X

augment(L1,{I})→L1

augment(L2,{Y1})→L2

End

Plot1(xyLine,L1,L2)

ZoomStat

Be sure to use
quotations when entering the function.
Remember that X in this case represents 10^x. Below are example plots.

y = x / 2 |

Try it, I hope
you find this helpful. Thank you for
your support and comments. See you next
time,

Eddie

This blog is
property of Edward Shore, 2017

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