Comments on: Where Does That Variable Come From? http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/ This blog is about Simulink. Mon, 13 Feb 2012 09:45:18 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Amy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1208 Amy Fri, 03 Sep 2010 22:04:14 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1208 @Guy, Thanks for the tip. I suspected that was the best option, but I'm not as familiar with the way Simulink works and wanted to be sure I was doing the calculations optimally. Best, Amy @Guy,

Thanks for the tip. I suspected that was the best option, but I’m not as familiar with the way Simulink works and wanted to be sure I was doing the calculations optimally.

Best,

Amy

]]> By: liang http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1206 liang Thu, 02 Sep 2010 06:04:23 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1206 UNABLE TO EVALUATE WORKSPACE PARAMETER UNABLE TO EVALUATE WORKSPACE PARAMETER

]]> By: Guy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1204 Guy Wed, 01 Sep 2010 19:23:59 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1204 @Amy, It is feasible to set the gain of a Gain block based on the value of another signal. However I do not recommend doing that. Typically in Simulink you have to types of data: - Signals: Intended to change every time step - Parameters: Intended to change not frequently Trying to set a parameter every time step is using it as a signal. Parameters are not designed to change every time step and doing that can sometimes lead to unexpected behavior. The recommended approach is, as you mention, to implement your algorithm with signals for values changing every time step. For your example, it means using a Product block instead of a Gain block. I hope this helps. Guy @Amy,

It is feasible to set the gain of a Gain block based on the value of another signal. However I do not recommend doing that. Typically in Simulink you have to types of data:

- Signals: Intended to change every time step
- Parameters: Intended to change not frequently

Trying to set a parameter every time step is using it as a signal. Parameters are not designed to change every time step and doing that can sometimes lead to unexpected behavior.

The recommended approach is, as you mention, to implement your algorithm with signals for values changing every time step. For your example, it means using a Product block instead of a Gain block.

I hope this helps.

Guy

]]> By: Amy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1203 Amy Wed, 01 Sep 2010 18:54:18 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1203 I have a tangentially related question. Is there a way to set the gain to a variable that is defined by inputs to the model? I'm running a simulation that receives streamed data from a separate computer during execution, and I'd like to stream the gain settings in real-time. I know I can just define my own gain block that does this calculation manually, but I was just curious if there was a way to use the built-in gain block. Thanks! I have a tangentially related question. Is there a way to set the gain to a variable that is defined by inputs to the model? I’m running a simulation that receives streamed data from a separate computer during execution, and I’d like to stream the gain settings in real-time. I know I can just define my own gain block that does this calculation manually, but I was just curious if there was a way to use the built-in gain block. Thanks!

]]> By: josy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1072 josy Wed, 28 Apr 2010 06:33:53 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1072 how can please answer me how to place empty subsystem in my model. josy_cp@yahoo.com how can please answer me how to place empty subsystem in my model.
josy_cp@yahoo.com

]]> By: josy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1071 josy Wed, 28 Apr 2010 06:33:10 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1071 how can i place empty subsystem in my model how can i place empty subsystem in my model

]]> By: Vipul http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1057 Vipul Thu, 15 Apr 2010 21:37:11 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1057 Hi Guy, I appreciate your response. I can not use 2nd suggestion of using "Clock" or "Digital Clock" block because the time in my data comes from data acquisition system. Actually this is a PWM type signal and I am trying to determine the time between two successive signal rises. If I used your first suggestion, the problem arises when I try to find rising or falling edge of the signal. A topic on simulink ‘From Workspace’ block with example would be worth discussing here. Thanks, Vipul Hi Guy,

I appreciate your response. I can not use 2nd suggestion of using “Clock” or “Digital Clock” block because the time in my data comes from data acquisition system. Actually this is a PWM type signal and I am trying to determine the time between two successive signal rises. If I used your first suggestion, the problem arises when I try to find rising or falling edge of the signal. A topic on simulink ‘From Workspace’ block with example would be worth discussing here.

Thanks,
Vipul

]]> By: Guy http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1050 Guy Thu, 08 Apr 2010 12:40:03 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1050 Hi Vipul, As the doc says for the From Workspace block, the first column is the time stamp at which the data of the other columns is outputted. One quick solution if you want the From Workspace block to output also a time signal is to create a 3 columns matrix where you will have [t t u]. However this might not be the best solution. Another way to think about it is that if you want time as a signal in your simulation you should use the "Clock" or "Digital Clock" block from the Sources section of the Simulink library. I hope this helps. Guy Hi Vipul,

As the doc says for the From Workspace block, the first column is the time stamp at which the data of the other columns is outputted.

One quick solution if you want the From Workspace block to output also a time signal is to create a 3 columns matrix where you will have [t t u]. However this might not be the best solution.

Another way to think about it is that if you want time as a signal in your simulation you should use the “Clock” or “Digital Clock” block from the Sources section of the Simulink library.

I hope this helps.

Guy

]]> By: Vipul http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1049 Vipul Wed, 07 Apr 2010 22:35:56 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1049 Hi Seth, I have a two column (time and signal value) array in my base workspace. I am trying to read this array with 'From Workspace' block in my model. I can read it but it gives me only one of the column value (signal value) from array. I would like to use the value from first column (time) based on certain conditions. Unfortunately, with this block I can not read time value (first column). Is there any specific way to do that? Am I using wrong block? Thanks. Hi Seth,
I have a two column (time and signal value) array in my base workspace. I am trying to read this array with ‘From Workspace’ block in my model. I can read it but it gives me only one of the column value (signal value) from array. I would like to use the value from first column (time) based on certain conditions. Unfortunately, with this block I can not read time value (first column). Is there any specific way to do that? Am I using wrong block?
Thanks.

]]> By: Jack http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1028 Jack Thu, 25 Mar 2010 13:25:11 +0000 http://blogs.mathworks.com/seth/2009/02/15/where-does-that-variable-come-from/#comment-1028 I know that the value is passed without code but if I want to retrieve my parameter value to make data range check validity, how can I do it ? Thanks for your answer I know that the value is passed without code but if I want to retrieve my parameter value to make data range check validity, how can I do it ?

Thanks for your answer

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