# Complex nonlinear decision boundary

**URL:** <https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173>\
**Category:** Supervised ML: Regression and Classification\
**Tags:** week-module-3\
**Created:** [October 24, 2023, 6:10am UTC](https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173 "2023-10-24T06:10:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![farhana\_hossain](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/farhana_hossain/32/73380_2.png) [@farhana\_hossain](https://community.deeplearning.ai/u/farhana_hossain)\
**Post date:** [October 24, 2023, 6:10am UTC](https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173/1 "2023-10-24T06:10:50Z")

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Hello,  
Andrew said in the week 3 decision boundary titled video that y = 1 is inside the boundary in the case of a complex nonlinear boundary. I couldn’t understand any specific reason behind this.  
Can anyone help me to understand this? I attached the screenshot.

 ![image](https://global.discourse-cdn.com/dlai/original/3X/9/9/995577c8f9466f3a0020abb28fa5dfe6e51953b9.png)

The video can be found at:  
[https://www.coursera.org/learn/machine-learning/lecture/qrxwU/decision-boundary](https://www.coursera.org/learn/machine-learning/lecture/qrxwU/decision-boundary)

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**Author:** ![TMosh](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/tmosh/32/9321_2.png) [@TMosh](https://community.deeplearning.ai/u/TMosh)\
**Post date:** [October 24, 2023, 6:33am UTC](https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173/2 "2023-10-24T06:33:31Z")

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Where the 1’s and 0’s lie depends entirely on the signs and magnitudes of the weights.

The sketch in the lecture is illustrating that a model with lots of polynomial terms can create a complex boundary. It’s not necessarily about which side of the boundary has the 1’s.

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<div class="post-metadata">

**Author:** ![farhana\_hossain](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/farhana_hossain/32/73380_2.png) [@farhana\_hossain](https://community.deeplearning.ai/u/farhana_hossain)\
**Post date:** [October 24, 2023, 10:13am UTC](https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173/3 "2023-10-24T10:13:13Z")

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Thanks a lot!

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<div class="post-metadata">

**Author:** ![TMosh](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/tmosh/32/9321_2.png) [@TMosh](https://community.deeplearning.ai/u/TMosh)\
**Post date:** [October 24, 2023, 5:22pm UTC](https://community.deeplearning.ai/t/complex-nonlinear-decision-boundary/476173/4 "2023-10-24T17:22:45Z")

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Closed on October 24, 2023, 5:22pm UTC