Reformatted and added analysis description

ANALYSES

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 ANALYSES
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+========
 
 This file lists the analyses currently implemented into ngspice.
 
-AC    : Small-signal frequency response analysis
+Table of Contents
 
-DC    : DC-sweep analysis
-        + Added resistance sweep as in spice 2.
-        * Note: It is possible to perform a generic parametric sweep ?
+ 1 Noise analysis (NOISE) 
+ 2 Operating point analysis (OP)
+ 3 Operating point sweep Analysis (DC)
+  3.1 Enhancements
+ 4 Pole-zero analysis (PZ)
+ 5 Small-Signal distortion analysis (DISTO)
+ 6 Small Signal frequency response analysis (AC)
+ 7 Sensitivity analysis (SENS)
+ 8 Transfer function analysis (TF)
+ 9 Transient analysis (TRAN)
 
-DISTO : Small signal distortion analysis
 
-NOISE : Noise analysis
 
-OP    : Operating point analysis
+1 Noise analysis (NOISE)
 
-PZ    : Pole-Zero analysis
+    The noise analysis does analysis device-generated noise for the given
+ circuit. When provided with an input source and an output port, the analysis 
+ calculates the noise contributions of each device (and each noise generator 
+ within the device) to the output port voltage. It also calculates the input 
+ noise to the circuit, equivalent to the output noise referred to the 
+ specified input source. This is done for every frequency point in a specified 
+ range - the calculated value of the noise corresponds to the spectral density 
+ of the circuit variable viewed as a stationary gaussian stochastic process.
+ 
 
-SENS  : Sensitivity analysis
+2 Operating point analysis (OP)
+
+    The operating point analysis determines the dc operating point of the 
+ circuit with inductors shorted and capacitors opened.
+
+
+3 Operating point sweep Analysis (DC)
+
+    The operating point sweep analysis determines the values of output 
+ variables while one or two specified independent voltage or current source is 
+ stepped over a user-specified range and the dc output variables are stored 
+ for each sequential source value.
+
+ 3.1 Enhancements
+  
+  Added resistance and temperature sweep.
+
+
+4 Pole-zero analysis (PZ)
+
+    The pole-zero analysis computes the poles and/or zeros in the small-signal 
+ ac transfer function. The program first computes the dc operating point and 
+ then determines the linearized, small-signal models for all the nonlinear 
+ devices in the circuit. This circuit is then used to find the poles and zeros 
+ of the transfer function. 
+
+
+5 Small-Signal distortion analysis (DISTO)
+
+    The distortion analysis computes steady-state harmonic and intermodulation 
+ products for small input signal magnitudes. Not all devices are supported.
+
+
+6 Small Signal frequency response analysis (AC)
+
+    The ac small-signal computes the ac output variables as a function of 
+ frequency. The program first computes the dc operating point of the circuit 
+ and determines linearized, small-signal models for all of the nonlinear 
+ devices in the circuit. The resultant linear circuit is then analyzed over a 
+ user-specified range of frequencies.
+
+
+7 Sensitivity analysis (SENS)
+
+    Ngspice will calculate either the DC operating-point sensitivity or the AC
+ small-signal sensitivity of an output variable with respect to all circuit 
+ variables, including model parameters. Spice calculates the difference in an 
+ output variable (either a node voltage or a branch current) by perturbing 
+ each parameter of each device independently.
+
+
+8 Transfer function analysis (TF)
+
+    The (small signal) transfer function analysis computes the dc small-signal
+ value of a transfer function (ratio of output variable to input source), 
+ input resistance, and output resistance is also computed as a part of the dc 
+ solution.
+
+
+9 Transient analysis (TRAN)
+
+    The transient analysis computes the transient output variables as a
+ function of time over a user-specified time interval. The initial conditions 
+ are automatically determined by a dc analysis. All sources which are not time 
+ dependent (for example, power supplies) are set to their dc value. 
 
-TF    : Transfer function analysis
 
-TRAN  : Transient analysis