# When you tutor math, the world brings an endless bounty of numerical comparisons. This specific one has not arisen during tutoring; yet, it might be the kind of summer distraction  a reader seeks.

Whether you are buying gasoline, or diesel, or electricity, you are buying energy. To develop perspective on society’s direction towards electric power, somewhat away from fossil fuels, one might ask, “What are the comparative prices of these sources of energy?”

Without doing any math, the sensible conclusion is that electricity is the cheapest form of energy. If it wasn’t, then private citizens would be tempted to buy generators to produce their own electricity. Yet, they don’t seem to be so tempted. Private citizens seem only to use generators when they don’t have access to “line” power. Such contexts are blackouts or remote camps.

Industry prefers diesel over gas, so it’s logical to conclude that, between the two, diesel must be a better bargain.

Let’s sharpen our pencils, then seek some confirmation of our suspicions.

Electricity: I’ve searched the net for the price of electricity in markets spread around North America. It seems that 12 cents per kWh is the US average, according to planet money.

Gasoline and Diesel: Wikipedia says that 1 gallon of gas contains around 33kWh of energy, whereas 1 gallon of the diesel at the pump contains around 38kWh. According to the U.S. eia, the “typical” June price for a gallon of gasoline was $3.69; for diesel, it was$3.91. From those numbers, the price per kWh for gasoline is $3.6933kWh=$0.11kWh or 11¢ per kWh. For diesel, it’s $3.9138kWh=$0.10kWh or 10¢ per kWh.

Well, according to the actual numbers, electricity might be the most expensive up against gas or diesel, while diesel, it turns out, is the cheapest. The prices are all potentially volatile; therfore, the comparisons may not turn out the same even next month. Regardless, I’m surprised.

The price comparisons above are “average” for June in the US. In a given local market, they may be different. Here on the BC coast in Canada, gas is around 16¢ per kWh, whereas household electricity works out to around 9¢ per kWh for typical family usage. So here, electricity is the much cheaper form of energy.

We are left with the question of why electricity seems to be gaining ground over fossil fuels, given the lesson above. Come back for more about energy comparisons in the near future. Here, we’re in another heat wave: enjoy the beautiful summer weather, and try to keep cool:)

Source: Fuel Oil, Wikipedia

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

# Tutoring math, you might be asked just about anything to do with numbers.  Here’s a comparison the tutor thinks might interest even the most casual visitor….

My automobile has just matured past its warranty. Though there’s seemingly nothing wrong with it, the idea of replacing it enters my mind now and again. Of course, there are choices now that weren’t viable when I bought this one. Notably, one might buy a hybrid vehicle now. What are the advantages?

Well, I’ve done some very rough calculations by way of comparing the “gas” option with the “hybrid” option. The makers of the Chevy Volt made it easy for me. However, I used Wikipedia as a source. It tells of a “combined” mileage of 62 mpg (or about 100km per 3.8L, if your prefer). From info I’ve picked up around the ‘net, you might expect around 30 to 35 mpg (32.5mpg=52km per 3.8L) from a typical gas-only vehicle, new, that’s around the size of the Volt.

# When you tutor computer programming, you must explain the use of variables.  Such is the next step of our PERL summer project.

To a computer, a value needs a name.  Computers (at this level) aren’t capable of changing context the way humans can; they need to be told what to do, and what to do it to, at every stage.

Here’s an example of the difference between humans and computers.  Suppose, for instance, you tell a grade 6 student the numbers 11 and 29, then ask them for the average.  The student will add the numbers, divide the sum by 2, then spontaneously say “The average is 20.”  If you ask the student to tell the original two numbers, they can; however, they realize that what you really want is the answer.

On the other hand, a computer needs to “identify” a value before it can do an operation to it.  Therefore, a computer program to find the average of 11 and 29 might proceed like this:

get the value of the first number:  call it number1

get the value of the second number:  call it number2

add number1 and number2; call the sum number3

divide number3 by 2; call the result theaverage

print out “The average is ” theaverage

In traditional programming, you name a variable first, then give it a value.  When you want the computer to manipulate that value, you refer to it by its variable name.  Planning a program, you don’t wonder what the answer will be; rather, you wonder how to explain to the computer what to do in order to find the answer.  Specifically, you need to tell it what steps to perform to which variables.  Actually working with the numbers is easy for a computer, once it has clear instructions.

Commonly, variable names are written as one word, even if they indeed contain more than one.  Therefore, thirdnumber might be a likely name for the third number referenced in a program; on the other hand, you might call it number3.  Digits can be used in variable names, but usually aren’t allowed as the first character.

In PERL, variable names are commonly given a dollar sign prefix; therefore, if you wanted to call a variable number3, you’d call it $number3. The dollar sign prefix increases program readability for humans; it’s easy to track what’s happening with the variables, since they all start with$.  There are other reasons, as well, for the \$ prefix on PERL variable names.

Next post, we’ll see some variables in action.  Enjoy your day:)

Source: Robert’s Perl Tutorial, by Robert Pepper.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

# Tutoring PERL beginnings, the details can be so important.  While the tutor now focuses to the Linux/Mac side, Windows users might do well to tune in.

Over my last few posts I’ve been discussing how to get started with PERL programming.  Of course, I’ve run parallel posts:  some have focused on Windows, others on Linux/Mac.  I hope you’ve all been successful in following the procedures I’ve offered.

Whichever world you reside in – assuming it is just one – knowing what’s going on in the other world often seems beneficial.  Therefore, I recommend the users of one operating system read the posts for the other, if only to realize how similar the procedures are.

Today’s emphasis is on the line

#!/usr/bin/perl

which is part of the script for Linux/Mac, but is conspicuously absent at the head of the script for Windows.

According to Robert Pepper’s Perl Tutorial, #!/usr/bin/perl is called the “shebang” line. (By the way: almost everything I know about PERL I learned from Robert Pepper.) He goes on to explain that under Unix systems (Linux is a derivative), the shebang line tells the file type so the computer knows how to execute it.

Windows, he continues, does not need a shebang line. However, a shebang line for the Windows script might look similar to this:

#!c:/strawberry/perl/bin/perl.exe

(The above shebang reveals the use of Strawberry Perl).

The line tells the location of the perl interpreter, which will execute the script. Once again, the line is not needed in Windows.

For Linux/Mac, however, you will see something like

#!/usr/bin/perl

at the head of a PERL script, and it is needed – on mine, anyway. Now you know why, whichever operating system you might use:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

# In the context of tutoring, a lazy summer day might mean academic pursuits at a relaxed pace.  The tutor acknowledges the need to bring Linux and Mac users equal with Windows users:  in this installment, he offers instructions for Linux and Mac users to execute their first PERL script.

In my previous post I instructed Windows users through the execution of their first PERL script. Now, Linux and Mac users, it’s your turn.

Open your text editor and type in the following:

#!/usr/bin/perl

print “Hello, how are you?–from PERL!\n\n”;

Let’s imagine you call your file july101 and save it in your “My_perl_programs” folder. In my experience, you can save it as type “all files” or type “text files” – just as long as it’s actually plain text.

Now, open your terminal and go into your “My_perl_programs” directory. Enter the command ls to make sure your file july101 is listed. Assuming you see it, enter the following command:

perl july101

If the process works, the terminal should reply with

Hello, how are you?–from PERL!

If you receive that greeting, congratulations! You, Linux or Mac user, have successfully executed your first PERL script.

The next few posts, we’ll review what we did during this one and last one. To quote Phil Collins in his hit song Against All Odds:

“There’s so much I have to say to you/So many reasons why….”

We’ll get to it all, in the coming days:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.