<p>In <em>the</em> Mundel Fleming model it is not constant. You must be working with some simplified version of Mundel Fleming model.</p>
<p>If Y is held fixed that means something else has to change when I changes. In your example, only other thing that is not fixed is the consumption function <span class="math-container">$C(.)$</span> so when I increases something must happen there. Maybe marginal propensity to consume decreases or autonomous consumption shrinks. The source of the model should explain its assumptions.</p>

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2022-09-09T14:37:51.183Z
Hi, thank you for your answer! So, in this case I(r) is constant? In addition, how can C(.) not be constant, when it depends on Y̅ and T̅, which are both constant variables C(Y̅–T̅)? Thanks!
student
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2022-09-09T14:43:15.993Z
C(.) is a function, for example C(Y-T) could look like $C=c_0+ c_1(Y-T)$ assuming linear consumption function. The parameters $c_0$ and $c_1$ could change if you allow them to be for the sake of the problems variables.
1muflon1
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2022-09-09T15:11:23.263Z
@student you are welcome if the above answer answered your question consider accepting it
1muflon1
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2022-09-10T05:34:32.650Z
How do I accept it?
student
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2022-09-10T09:57:28.037Z
@student you can click on the tick below upvote button. You should also consider doing that for other people who answered your questions
1muflon1
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2022-09-11T08:47:16.017Z
Hi muflon, do you have any idea why I can' post with this account? Thanks.
student
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2022-09-11T12:32:52.503Z
@student i am not sure what you mean? Please make a post about it on our meta page and describe the problem in detail
1muflon1
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2022-09-12T07:14:52.283Z
I meant that I can't ask questions with this account.
student
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2022-09-13T08:41:56.010Z
@student hi please post about it on our meta site
1muflon1
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2022-09-16T10:23:42.500Z
@student even if you can’t post here you should be able to post on the economics.meta stack exchange
1muflon1
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2022-09-09T12:43:59.913Z
2022-09-09T12:43:59.913Z
1muflon1
<p>Since I(r) is not constant, how could Y be constant on the left side of the equation of the goods market equilibrium - IS curve function?</p>
<p>Thank you!</p>
<p>Ps: I don't know where I should write function, or equation, so sorry about that.</p>

<macroeconomics><mathematical-economics><economic-growth>
Why is Y constant on the left side of the equation : Y̅=C(Y̅–T̅)+I(r)+G̅, of the Mundell Fleming model?
student
# Why is Y constant on the left side of the equation : Y̅=C(Y̅–T̅)+I(r)+G̅, of the Mundell Fleming model?

(Asked by: username_0 on 2022-09-09)

Since I(r) is not constant, how could Y be constant on the left side of the equation of the goods market equilibrium - IS curve function?

Thank you!

Ps: I don't know where I should write function, or equation, so sorry about that.

**Tags:** macroeconomics, mathematical-economics, economic-growth

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## 1 answers

### Answer by username_1 on 2022-09-09. Score: 1

In *the* Mundel Fleming model it is not constant. You must be working with some simplified version of Mundel Fleming model.

If Y is held fixed that means something else has to change when I changes. In your example, only other thing that is not fixed is the consumption function $C(.)$ so when I increases something must happen there. Maybe marginal propensity to consume decreases or autonomous consumption shrinks. The source of the model should explain its assumptions.

> **Comments:**
> **username_0**: Hi, thank you for your answer! So, in this case I(r) is constant? In addition, how can C(.) not be constant, when it depends on Y̅ and T̅, which are both constant variables C(Y̅–T̅)? Thanks!  
> **username_1**: C(.) is a function, for example C(Y-T) could look like $C=c_0+ c_1(Y-T)$ assuming linear consumption function. The parameters $c_0$ and $c_1$ could change if you allow them to be for the sake of the problems variables.  
> **username_1**: @student you are welcome if the above answer answered your question consider accepting it  
> **username_0**: How do I accept it?  
> **username_1**: @student you can click on the tick below upvote button. You should also consider doing that for other people who answered your questions  
> **username_0**: Hi muflon, do you have any idea why I can' post with this account? Thanks.  
> **username_1**: @student i am not sure what you mean? Please make a post about it on our meta page and describe the problem in detail  
> **username_0**: I meant that I can't ask questions with this account.  
> **username_1**: @student hi please post about it on our meta site  
> **username_1**: @student even if you can’t post here you should be able to post on the economics.meta stack exchange  

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