All posts by Kenji

I’ve compiled a guide on generating options tags using options_for_select.

Environment

Ruby 2.2.3
Rails 4.2.5

Continue reading →

Code

(日本語) Rails: クラス名が ActiveRecord::AttributeMethods 内のモジュールと同じ場合

Tuesday December 8th, 2015 Kenji

Sorry, this entry is only available in 日本語.

Code

CoffeeScript: How to write For Loop

Sunday December 6th, 2015 Kenji

How to write for loop in CoffeeScript.

for loop of array

In Ruby, it is written as items.each.

arr = ['a', 'b', 'c']
for item in arr
alert item

arr = ['a', 'b', 'c']

for item in arr

alert item

for loop of array with index

In Ruby, it is written as items.each_with_index.

arr = ['a', 'b', 'c']
for item, index in arr
alert index
alert item

arr = ['a', 'b', 'c']

for item, index in arr

alert index

alert item

Mathematics

Proof: Irrational numbers $a$ , $b$ exist that make $a^b$ rational number

Sunday December 6th, 2015 Kenji

Irrational numbers ( a ) , ( b ) exist that make ( a^b ) rational.

Prove with law of excluded middle and without fixing what ( a ) and ( b ) are.

Proof

Supporse ( x = sqrt{2} ^ sqrt{2} ) .

Case: ( x ) is Rational

( sqrt{2} ) is irrational, so ( a = b = sqrt{2} ) make ( a^b ) rational. ( ( sqrt{2} ) が無理数であることの証明は証明: ( sqrt{2} ) は無理数をご覧ください。)

Case: ( x ) is Irrational

begin{eqnarray*} sqrt{2} & = & (sqrt{2}^sqrt{2})^sqrt{2} & = & sqrt{2}^{sqrt{2} cdot sqrt{2}} & = & sqrt{2}^2 & = & 2 end{eqnarray*}

Then, ( a = x = sqrt{2}^sqrt{2} ) and ( b = sqrt{2} ) are irrational and make ( a^b ) rational.

Above all, there are irrational numbers ( a ) and ( b ) that make ( a^b ) rational.

Linux

OpenShift: What rhc setup does?

Thursday December 3rd, 2015 Kenji

We can use the command rhc setup with OpenShift server. I tried it, and wrote what the command do.