# Questions tagged [linear-systems]

A linear system operates on inputs with only linear operators so the response to a complex input can be analysed as the sum of the response to a set of simpler inputs. This mathematical property makes the analysis of linear systems much simpler than non-linear systems where this summation or superposition does not hold. Linear systems are generally further classified as time invariant, meaning that there characteristics do not change over time.

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### Fit a line pattern on curve with unknown number of points

I've got a sample curve which ends theoretically with decreasing exponential. The curve end falls into noise. The sample points are given in log scale. What I want to do, is to find and fit the linear ...
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### Do Causal Discrete-time systems have proper transfer functions?

In the case of continuous-time systems, if the system is causal, its Laplace transfer function is strictly proper (the degree of the numerator is less than the degree of the denominator). Is this ...
403 views

### Can I see from the PSD if a system is a LTI system?

I am studying the meaning of the power spectral density (PSD) and I am wondering whether I can see from the PSD of the input signal and output signal if a system is a LTI system?
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### Is this HW question even valid? (linear systems)

The question is: Are the following systems linear time invariant? $y(t)=x(t)$, with $x(t)=u(t)$ (unit step function) $y[n]=x[n]$, with $x[n]=\delta[n]$ (Dirac delta function) The reason I am asking ...
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### Is digital up and down sampling linear/causal/time-invariant?

So I am trying to determine whether the process of up sampling (zero padding) and downsampling are linear, causal and/or time-invariant. Based on some resources I found online, I am under the ...
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### How do I take the real part of this bandpass filter system's output?

I'm stuck on a final step in this problem. Essentially, there are the two systems above, which we'll call System 1 (Fig. 4.26, with ideal lowpass $H(jw)$) and System 2 (with $H_1(jw)$). The question ...
377 views

### Does instability make an otherwise LTI system nonlinear (or time-variant)?

I am spinning this question off from the question from johnny. Matt L. and I have had directly opposite conclusions to johnny's question. I want to decouple the question from issues of causality and ...
160 views

### How to periodically estimate states of a LTI if the output is measured irregularly?

How can I periodically estimate the states of a discrete linear time-invariant system in the form $$\dot{\vec{x}}=\textbf{A}\vec{x}+\textbf{B}\vec{u}$$ $$\vec{y}=\textbf{C}\vec{x}+\textbf{D}\vec{u}$$...
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### Is this system linear?

I have this system: $$y[n] = -\frac{1}{2} x[n+2] - y[n+1]$$ I have no idea how to prove if the system is linear or not, because, it depends on future outputs... Thanks for the help
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### Checking linearity/time-invariance etc. for recursive system

I'm familiar with the general methodology for checking if a system is linear: Define output $y_1[n]$ for input $x_1[n]$, define output $y_2[n]$ for input $x_2[n]$ Define $x_3[n] = ax_1[n] + bx_2[n]$ ...
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### Natural, Forced and Total System Response - Time domain Analysis of DT

I am a self-learner of DSP by reading related books. While reading Time domain Analysis of DT (Discrete Time) system, I suddenly got introduced to difference equation representing a system. It then ...
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### Time variant and Time Invariant Systems

I was trying to solve the below system is a Time variant or Time Invariant System: $y(n)=nx^{2}(n)$ Now for a system to be time invariant the system property should be : ...
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### What Are Some Examples of Applications of LTI Systems

I'm giving a lecture on LTI systems. I encountered some questions: for a discrete LTI system H with impulse response h, is the system applied on signal x(t) equals x*h - normal discrete convolution ...
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### Low dimensional system identification algorithms

I'm a physics Phd student and just have a self-taught knowledge about lti-systems. After a while I found out that several techniques such as heat capacity or thermal-conductance measurements can be ...
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### Introduction to Clustering and Classification of Linear Sequence

I'm a programmer/engineer that is getting into developing prototype wearable technology. I would like to be in a position to interpret raw accelerometer data and categorised the data into activities ...
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### Impulse response of the inverse system to the backward difference

I'm currently stuck on a problem. I have a DT LTI system $\mathcal{T}$ that depicts the first backward difference: $$y[n] = \mathcal{T} \{ {x[n] \} } = x[n] - x[n-1]$$ Its impulse response is ...
215 views