It is a function that measures the performance of a Machine Learning model for given data. Cost Function quantifies the error between predicted values and expected values and presents it in the form of a single real number. Depending on the problem Cost Function can be formed in many different ways. The purpose of Cost Function is to be either:
Minimized - then returned value is usually called cost, loss or error. The goal is to find the values of model parameters for which Cost Function return as small number as possible.
Maximized - then the value it yields is named a reward. The goal is to find values of model parameters for which returned number is as large as possible.
Gradient descent :
an algorithm called gradient descent for minimizing the cost function.
It turns out gradient descent is a more general algorithm, and
is used not only in linear regression.
It's actually used all over the place in machine learning.
And later in the class, we'll use gradient descent to minimize
other functions as well, not just the cost function J for the linear regression
Andreu NG coursera.com 1week (*****) to see the gradient descent. -- Firstly try to understand the cost function and gradient for one variable/ one parameter/ one dimensional.
Angular CLI is abbreviated for Angular command line interface.
Angular CLI creates the ideal Angular environment for your Angular app. It includes all the importing, packaging, BrowsLinks using Webpack all by itself.But
there is no need for you to know what is a Webpack or how it works,
because all of the webpack configuration is completely done by Angular
CLI thus it takes all that burden off of the developer's shoulders.
Angular cli makes it easier to work in angular environment. As it contains whole bunch of commands to create core building blocks of angular and to even unit -testing them.
CLI is shipped with WebPack which bundles javascript and css files dynamically and add them to index. html like main.bundle.js , polyfill.bundle. js etc. .
webpack is powerful. It is incredibly configurable. However, this power and flexibility can make for a rather steep learning curve.
Learning about webpack is one of the major hurdles to getting up and running with modern JavaScript frameworks like React and Angular. The nice folks on the Angular team wanted to make it easier for people to start using Angular.
They did this by embedding webpack in the Angular CLI.
Now, as an Angular developer you don’t need to know anything about
webpack. The Angular CLI hides all that webpack complexity. However,
that simplicity comes at the price of flexibility. By using the Angular
CLI you lose the ability to configure and customize webpack.
webpack is a static module bundler for modern JavaScript applications
In webpack you configure the following:
Entry: the module where webpack should start
Output: where webpack emits the bundles it creates
Loaders: enable webpack to process more than just JavaScript files
Plugins: perform a wide range of tasks like minification, for example
You set all these up in the webpack configuration file which is typically named: webpack.config.js
So Where is the webpack.config.js?
“But
wait Todd, I just searched my entire Angular project and there is no
webpack.config.js. Are you sure Angular CLI still uses webpack?”
OK, you’re right, there is no webpack.config.js
in our Angular project. And, some healthy skepticism is a good thing.
But, let’s take a quick look and verify that Angular does in fact depend
on webpack.
In our project we can find a local copy of the Angular CLI here: node_modules\@angular\cli
In that directory you should see the package.json file for Angular CLI. Open it and take a look at the dependencies and among others you will see webpack, webpack-dev-server, etc. For example:
Also, in node_modules you can see that these webpack based dependencies actually did get installed. For example: node_modules/webpack So, we see that Angular CLI is, in fact, using webpack
but it is only a black box to us. This is great if you aren’t a webpack
expert. But, if you have taken the time to level-up your webpack
skills, this might be unacceptable to you. Fear not, the Angular CLI has
a solution for us.
NPM and Yarn
These
two technologies solve the exact same problem. To be more concrete,
Yarn is a superset of NPM that solves many problems that NPM has. So
what are these for?
NPM
stands for Node Package Manager. It is what its name describes. It is a
package manager for Node based environments. It keeps track of all the
packages and their versions and allows the developer to easily update or
remove these dependencies.
Babel
As
any language, Javascript also has versions named ECMAScript (short for
ES). Currently, most browsers support ES5. ES5 used to be good even
though it was painful to code in it. Remember, this
not reading from inside callback functions? The new version of
Javascript, ES6, also known as ES2015 (specs of the language were
finalized in June 2015) makes Javascript great again. If you want to
learn about ES6, check out the links at the end of this article. All the
great features of ES6 come with one big problem — majority of browsers
do not fully support them. That’s when Babel comes to play. Babel is a JS transpiler that converts new JS code into old ones. It is a very flexible tool in terms of transpiling. One can easily add presets such as es2015, es2016, es2017, so that Babel compiles them to ES5.
Webpack
Now
that we know what Babel and ES6/7 are, we would like to use that. We
would also like to use SASS for our styles, PostCSS for autoprefixing.
Plus, we would like to minify and uglify both our CSS and Javascript
code. Webpack solves all of these problems using one config file (named webpack.config.js) and one CLI command webpack.
Webpack
is a modular build tool that has two sets of functionality — Loaders
and Plugins. Loaders transform the source code of a module. For example,
style-loader adds CSS to DOM using style tags. sass-loader compiles SASS files to CSS. babel-loader
transpiles JS code given the presets. Plugins are the core of Webpack.
They can do things that loaders can’t. For example, there is a plugin
called UglifyJS that minifies and uglifies the output of webpack.
Rule 1: @Inputs: Input properties value will be changed when its ref will be changed
Rule 2: A component have own internal state. in the ts file , if value change due to api or set-timeout it will not show in html page directly. it only show when any event(click, change) occur from the html page.
Rule 3: We run change detection explicitly. The first is detectChanges() which tells Angular to run change detection on the component and his children.
Rule 4: Angular Async Pipe. The async pipe subscribes to an observable or promise and returns the latest value it has emitted
see the example of above link
If a component depends only on its input properties, and they are observable, then this component can change if and only if one of its input properties emits an event.
Rule 5: onPush and View Queries.
@Input() set content(value) { this._content = value; this.cdr.markForCheck(); }
Rule 6: === onPush++ (VVVVIIIIII)
Also, by creating a dedicated component we make our code more readable and reusable.
