Here are some of the Meetup groups that I have participated in:

Plano Software Entrepreneurs Meetup

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# Category: Uncategorized

## Meetup Groups in the DFW Area

## Renogy Rover Monitoring with the Raspberry Pi

## Gibraltar Pictures

## Canon MF4150 Printer in Ubuntu 9.04

## Finding Probabilities Using the Central Limit Theorem – #2

## Finding Probabilities Using the Central Limit Theorem

## Standard Error Definition

## Monthy ARM Reset Schedule

Business, Tech, and Facts…

Here are some of the Meetup groups that I have participated in:

Plano Software Entrepreneurs Meetup

The information, below, was posted on the Renogy Forum by a user with the screenname *lindsey*. The forum recently moved and the documentation was temporarily lost. The information was reposted; but I wanted to put it here for easy reference in case it gets lost again.

This information is about connecting the Renogy Rover to the Raspberry Pi for monitoring.

First, here is a general link discussing connection of the Raspberry Pi to a solar battery charger.

https://www.rototron.info/raspberry-pi-solar-serial-rest-api-tutorial/

Here is the wiring diagram that the Renogy Forum post provided:

Here is a sample output on an Android from the Python scripts.

Here is a sample database query.

The diagram, below, is a diagram of how the Rover’s RJ-12 port splits out into RS-232 signals. Note that only TX, RX, and ground are used.

The link below was put together by *lindsey.* It describes the needed hardware (in addition to the Pi) as well as the general functionality of the Python code.

Finally, here is a zip file with the Python code. Unfortunately, I do not have a way to contact *lindsey*. The code comments say that her name is Lindsey Crawford. If anyone knows how to contact her, please let me know.

Download the following file:

http://www.rainmall.com/MF4150/CNCUPSMF4100ZK.ppd

Open a terminal.

cd /tmp

sudo cp CNCUPSMF4100ZK.ppd /etc/cups/ppd

sudo cp pstoufr2cpca /usr/lib/cups/filter/

Open Firefox and go to the following URL: http://localhost:631/

Click Add Printer

Enter a Name, Location, and Description. These can be anything you like. I made my name “MF4150”, location “HALL”, and Description “MF4150 Printer”.

Click Continue.

For Device, choose LDP/LPR Host or Printer. Choose Continue.

Choose URI of lpd://192.168.72.2/MF4100Series

Choose Continue.

Under “Or Provide a PPD File” type in: /etc/cups/ppd/CNCUPSMF4100ZK.ppd

Click Add Printer.

You may be asked for a username and password. If so, use your root user name and password.

Finally, you should see a notice that the printer has been added successfully. The screen will evenually refresh.

Click the “Home” button on the CUPS web configuration page. Then, click the button that says “Manage Printers”.

In terminal: sudo chmod 755 /var/spool/cups

Clock “Print Test Page”.

**In a population μ _{Y} = 100 and σ_{ Y}^{2} = 43. In a random sample of size n = 64, what is Pr (101 < Ȳ < 103)?**

The sample variance = (σ_{ Y}^{2} / n) = 43/64 = 0.671875

Therefore, the Standard Error (SE) = sqrt(0.671875) = 0.81968.

Normalizing this to a Standard Normal Distribution,

Z = ((103 – μ_{Y}) / SE)

Z = ((103 – 100) / 0.81968) = 3.66

The Z value is the number of Standard Errors away from the mean that will yield the desired Ȳ value of 103.

This is a one sided hypothesis since we are interested in the probability of Ȳ being < 103.

In EXCEL, the probability that Ȳ is < 103 is:

=NORMDIST(Z-Value, Mean of 0, Standard Deviation of 1, 1 for Cumulative)

=NORMDIST(3.66, 0, 1, 1)

=0.999874

Using the same logic for the probability of Ȳ being < 101,

Z = ((101 – μ_{Y}) / SE)

Z = 1 / 0.81968 = 1.22

NORMDIST(1.22, 0, 1, 1) = 0.8888

The difference between the two is the probability of Ȳ being between 101 and 103.

Answer: 0.1111

**In a population μ _{Y} = 100 and σ_{ Y}^{2} = 43. In a random sample of size n = 100, what is Pr (**

The sample variance = (σ_{ Y}^{2} / n) = 43/100 = 0.43

Therefore, the Standard Error (SE) = sqrt(0.43) = 0.6557.

Normalizing this to a Standard Normal Distribution,

Z = ((101 – μ_{Y}) / SE)

Z = ((101 – 100) / 0.6557) = 1.525

The Z value is the number of Standard Errors away from the mean that will yield the desired Y value of 101.

This is a one sided hypothesis since we are interested in the probability of Y being < 101.

In EXCEL, the probability that Y is < 101 is:

=NORMDIST(Z-Value, Mean of 0, Standard Deviation of 1, 1 for Cumulative)

=NORMDIST(1.525, 0, 1, 1)

=0.9364

__What is the difference between the sample average, Ȳ, and the population mean?__

The sample average is the average of the samples taken from a population. The population mean is the average of the entire population. They are guaranteed to be the same if and only if the sample includes the entire population.

**What is the difference between the estimator and the estimate?**

The estimator is a function of the sample data. The sample data is drawn randomly from the population. The estimator is a function that is used to make an educated guess of one of the parameters in the population such as the population mean. And example of the estimator is a function that produces Ȳ where Ȳ is the sample mean. For example, if n samples are taken from a population of 10 things, Ȳ = (1/n) * sum(X1 + X2 + X3 + X4) where X1, X2, X3, and X4, are the sample values. The population mean itself = (1/10) * sum(X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8 + X9 + X10).

In this case, the estimator is the function (1/n) * sum(X1 + X2 + X3 + x4).

**Assume that a population distribution has a mean of 10 and a variance of 16. Determine the mean and variance of Ȳ from an i.i.d. sample from this population for n = 10.**

The mean of the population sample is expected to be 10. The variance of Ȳ is expected to be = (Population Variance / n) = 16/10 = 1.6. Obviously, as we take more and more samples from the population, the variance of the sample mean will converge toward zero. For example, if we take 1000 samples, the variance of Ȳ , the sample mean, will be 0.016. By this point, we can be reasonably sure that the sample mean is very close to 10.

The fact that the sample variance approaches 0 with large numbers of samples (n) and that the sample mean approaches the population mean is a result of the Law of Large Numbers.

**What role does the central limit theorem play in hypothesis testing in statistics? What role does it play in the construction of confidence intervals?**

Due to the Central Limit Theorem, the distributions of sample means for multiple samples of a population is, itself, a distribution. The distribution of the sample means is approximates a Normal Distribution if there are enough samples. Because of this, confidence intervals can be constructed using standard deviations around the sample mean. For example, (±1.96 * (Sample Mean Standard Deviation)) gives us a 95% certainty that the population mean falls within a set of values.

How many samples are “enough?” Well, it depends on how the population values are distributed. But, usually 30 samples are enough to construct a reasonable approximation to the Normal Distribution.

**What is the difference between a null hypothesis and an alternative hypothesis?**

A null hypothesis is a value that is chosen and assumed to be true. The alternate hypothesis is a value that is chosen and assumed to be true if the null hypothesis is false.

**What is the “size of a test?”**

The size of a test is the probability that a test rejects the null hypothesis even though the null hypothesis is really true.

**What is the significance level?**

A person chooses a significance level for a test (e.g., 50%, 75%, 90%, 95%, or 99%) and uses it as a criteria to reject a hypothesis test if the null hypothesis is true.

**What is the definition of “power?”**

The power is the probability that a test rejects the null hypothesis when the alternative hypothesis is true.

**What is the difference between a one sided and a two sided alternative hypothesis?**

With a one sided hypothesis, the value of interest is only on one side (> or <) the null hypothesis. Under the two sided alternate hypothesis, the value of interest is not equal to the null hypothesis value.

**Why does a confidence interval contain more information than the result of a single hypothesis test?**

The confidence interval contains all values that reject the null hypothesis. Since the sample mean is normally distributed, then the confidence interval contains values that are at least a given amount larger than the sample mean as well as values that are at least a given amount smaller than the sample mean.

**Why is the differences-of-means estimator, applied to data from a randomized controlled experiment, an estimator of the treatment effect?**

The “treatment effect” is the causal effect in an experiment or quasi-experiment. The causal effect is the expected effect of a given treatment or intervention in an ideal randomized controlled experiment. An example of a “treatment effect” is the expected result of giving a drug to a population versus not giving it to an identical population. Another example is the expected result of giving fertilizer to plants versus not giving it to other plants growing in otherwise identical conditions.

The differences-in-mean estimator is the differences in mean between the control groups (those that have not received the treatment) and the treatment groups. Remember, for such experiments to have any meaning, the control group and treatment group must be randomly selected from the sample (identical) population.

The **standard error** of an estimation is the estimated standard deviation of the error in the estimation. Specifically, it estimates the standard deviation of the difference between estimated values and the true values.

Notice that the true value of the standard deviation in a population is usually unknown and the use of the term *standard error* carries with it the idea that an estimate of this unknown quantity is being used. It also carries with it the idea that it measures, not the standard deviation of the estimate itself, but the __standard deviation of the error in the estimate__, and these can be very different.

where

*s*is the sample standard deviation (i.e., the sample based estimate of the standard deviation of the population), and*n*is the size (number of items) of the sample.

We’re half way through the sub-prime resets.