# Hello, how does ampl write a log base of 0.1

**URL:** <https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915>\
**Category:** Support\
**Created:** [January 21, 2024, 6:44am UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915 "2024-01-21T06:44:02Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![liangzilu\_liangzilu](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/liangzilu_liangzilu/32/408_2.png) [@liangzilu\_liangzilu](https://discuss.ampl.com/u/liangzilu_liangzilu)\
**Post date:** [January 21, 2024, 6:44am UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915/1 "2024-01-21T06:44:02Z")

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Hello, I want to represent the logarithm of different base numbers,  
but the ampl explanation document seems to only have log10 and log,  
I want to represent the constraint how to do?

 ![image](https://us1.discourse-cdn.com/flex019/uploads/ampl/original/1X/2033edc8a1bfb5d809f0917410ddd8a0c5fdf406.png)

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<div class="post-metadata">

**Author:** ![liangzilu\_liangzilu](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/liangzilu_liangzilu/32/408_2.png) [@liangzilu\_liangzilu](https://discuss.ampl.com/u/liangzilu_liangzilu)\
**Post date:** [January 22, 2024, 7:39am UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915/2 "2024-01-22T07:39:50Z")

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Hello, I wrote this is wrong, there is a mistake, may I ask how to express the above formula

![image](https://us1.discourse-cdn.com/flex019/uploads/ampl/original/1X/fb0908ebad5bb15a7c8f53fa65bc45e8b4f140c1.png)

![image](https://us1.discourse-cdn.com/flex019/uploads/ampl/original/1X/3c78dc3caa026e7145a31a722c1f27223522e923.png)

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**Author:** ![4er](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/4er/32/530_2.png) [@4er](https://discuss.ampl.com/u/4er)\
**Post date:** [January 22, 2024, 7:49pm UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915/3 "2024-01-22T19:49:38Z")

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\log\_\frac{1}{10} (e^x+10^R) has the same value as -\log\_{10} (e^x+10^R), so you can write this constraint as

y + R \leq -\log\_{10} (e^x+10^R)

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<div class="post-metadata">

**Author:** ![liangzilu\_liangzilu](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/liangzilu_liangzilu/32/408_2.png) [@liangzilu\_liangzilu](https://discuss.ampl.com/u/liangzilu_liangzilu)\
**Post date:** [January 23, 2024, 12:41am UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915/4 "2024-01-23T00:41:59Z")

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Hello There is an error when x goes to infinity, how do I set the upper and lower bounds of y

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**Author:** ![4er](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/4er/32/530_2.png) [@4er](https://discuss.ampl.com/u/4er)\
**Post date:** [January 24, 2024, 4:59pm UTC](https://discuss.ampl.com/t/hello-how-does-ampl-write-a-log-base-of-0-1/915/5 "2024-01-24T16:59:47Z")

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You can add a constraint to your AMPL model to set a lower bound or an upper bound on a variable, or on an expression involving variables.