Wednesday, January 19, 2011

Matlab: Vector product, multiply 2 column matrices, "element-wise" multiplication

If we have 2 column matrices A, B.
>>A = [10;20;30]
A =
10
20
30

>> B = [1;2;3]
B =
1
2
3

>> A+B
ans =
11
22
33

>> A*B
??? Error using ==> mtimes
Inner matrix dimensions must agree.

In order to perform "element-wise" operations, we have to use ".", so for multiplication ".*", division "./"

>> A.*B
ans =
10
40
90

>> A./B
ans =
10
10
10

CakePHP : Error: The requested address “/” was not found on this server

I was moving my cakephp application to a new server and had this issue: Error: The requested address “/” was not found on this server.

The following keys might resolve your issue:

1. Check your DATABASE_CONFIG (/app/config/database.php)
2. Delete all the cache files from all of your tmp subfolders (/app/tmp)
3. Make sure your /app/tmp folder (and all of its sub folders) are writable

If you still have issues with the app, you might have to change the debug switch to 2 or 3 in the /app/config/core.php

Find the line which says "Configure::write" and replace with the following:
Configure::write('debug', 3);

This would spit all the errors on your webpage. You can debug from there.

Mac: removing known hosts/ ssh-rsa keys /RSA key fingerprint.

1. Open known_hosts file located at  /Users/username/.ssh/known_hosts or ~/.ssh/known_hosts
2. Delete the CONTENTS of the file.

Since .ssh is a hidden folder, you can show/hide hidden folders using directions at mac-showhide-files-in-mac

Tuesday, January 18, 2011

Kernighan’s Law !

"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it."

Comparing Intel Core i3, i5, i7 processors

Intel Core i3
• Dual Core processor
• Hyper Threading Support (HT)
• Due to HT, this has 2 virtual cores.
2 physical cores, 2 virtual cores
• Turbo Boost (dynamic overclocking)
• Integrated graphics processor
• Fabrication : 32nm technology

Intel Core i5 – Dual Core
• Dual Core Processor
• Hyper Threading Support (HT)
• Due to HT, this has 2 virtual cores.
2 physical cores, 2 virtual cores
• Turbo Boost (dynamic overclocking)
• Integrated graphics processor
• Fabrication : 32nm technology

Intel Core i5 – Quad Core
• Quad Core Processor
4 physical cores.
• Turbo Boost (dynamic overclocking)
• Fabrication : 45nm technology

Intel Core i7
• Quad Core Processor
• Hyper Threading Support (HT)
• Due to HT, this has 8 virtual cores
4 physical cores, 8 virtual cores
• Turbo Boost Technology
• Fabrication : 45nm technology

Intel Core i7-980X and i7-970 have 6 physical cores and 12 virtual cores.

Monday, January 10, 2011

CakePHP: Multiple Inserts - Insert multiple rows using single statement.

Using the method saveAll(), we can achieve the desired goal. http://book.cakephp.org/view/75/Saving-Your-Data

Example:
If you want to save multiple records/rows into the same table.


$multipleRowData = Array(   
 Array('name' => 'Bob', 'phone' => "123-123-7777"),  
 Array('name' => 'Ann', 'phone' => "987-123-5555"),  
 Array('name' => 'Tom', 'phone' => "788-123-4569")  
 );   
 $this->Mymodelname->saveAll($multipleRowData);  


This would result in inserting 3 rows in the "mymodelname" table.

Sunday, January 2, 2011

CakePHP: Adding/deleting columns in the database after the application is Baked

If you had already baked the application and now if you made changes to the database by adding or deleting columns, then do the following:

1. Open "core.php" located at : app/config/core.php
2. Find the line which looks like: Configure::write('debug', 0);
3. Change it to Configure::write('debug', 2);
4. Refresh your application webpage.
5. Reset the line in core.php to Configure::write('debug', 0);

What basically this will do is refreshing the "model" cache.
Changing the debug level will ensure that all your databases changes are reloaded.

Following are the notes related to which debug level, you want to set.
/**
* CakePHP Debug Level:
*
* Production Mode:
* 0: No error messages, errors, or warnings shown. Flash messages redirect.
*
* Development Mode:
* 1: Errors and warnings shown, model caches refreshed, flash messages halted.
* 2: As in 1, but also with full debug messages and SQL output.
* 3: As in 2, but also with full controller dump. (NOTE: Not in CakePHP 1.3)
*
* In production mode, flash messages redirect after a time interval.
* In development mode, you need to click the flash message to continue.
*/

jQuery: Count number of visible divs

 $("div:visible").length  
 or  
 $("div:visible").size()  

If we need for a specific 'class', then

 $(".myclass div:visible").length  
 or  
 $(".myclass div:visible").size()