PID library giving nan out output

the mpu object is the accelerometer/gyroscope module. i didn't include most of the code for it because it would add alot of unimportant stuff. I can confirm that the code for the accelerometer/gyroscope is able to output a correct measurement of pitch angle in degrees in double data type. here is the full code in case you think it could be something in there.

#include <PID_v1.h>
#include "I2Cdev.h"
#include "MPU6050_6Axis_MotionApps20.h"
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
    #include "Wire.h"
#endif
MPU6050 mpu;
#define LED_PIN 13 // (Arduino is 13, Teensy is 11, Teensy++ is 6)
bool blinkState = false;
double Setpoint, Input, leftCorrection;
PID leftController(&Input, &leftCorrection, &Setpoint,2,1,1, DIRECT);
// MPU control/status vars
bool dmpReady = false;  // set true if DMP init was successful
uint8_t mpuIntStatus;   // holds actual interrupt status byte from MPU
uint8_t devStatus;      // return status after each device operation (0 = success, !0 = error)
uint16_t packetSize;    // expected DMP packet size (default is 42 bytes)
uint16_t fifoCount;     // count of all bytes currently in FIFO
uint8_t fifoBuffer[64]; // FIFO storage buffer

// orientation/motion vars
Quaternion q;           // [w, x, y, z]         quaternion container
VectorInt16 aa;         // [x, y, z]            accel sensor measurements
VectorInt16 aaReal;     // [x, y, z]            gravity-free accel sensor measurements
VectorInt16 aaWorld;    // [x, y, z]            world-frame accel sensor measurements
VectorFloat gravity;    // [x, y, z]            gravity vector
float euler[3];         // [psi, theta, phi]    Euler angle container
float ypr[3];           // [yaw, pitch, roll]   yaw/pitch/roll container and gravity vector

// packet structure for InvenSense teapot demo
uint8_t teapotPacket[14] = { '

, 0x02, 0,0, 0,0, 0,0, 0,0, 0x00, 0x00, '\r', '\n' };

// ================================================================
// ===              INTERRUPT DETECTION ROUTINE                ===
// ================================================================

volatile bool mpuInterrupt = false;    // indicates whether MPU interrupt pin has gone high
void dmpDataReady() {
    mpuInterrupt = true;
}

// ================================================================
// ===                      INITIAL SETUP                      ===
// ================================================================

void setup() {
  leftController.SetOutputLimits(0, 10);
  Setpoint=0;
    // join I2C bus (I2Cdev library doesn't do this automatically)
    #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
        Wire.begin();
        TWBR = 24; // 400kHz I2C clock (200kHz if CPU is 8MHz)
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        Fastwire::setup(400, true);
    #endif

// initialize serial communication
    // (115200 chosen because it is required for Teapot Demo output, but it's
    // really up to you depending on your project)
    Serial.begin(115200);
    while (!Serial); // wait for Leonardo enumeration, others continue immediately

// NOTE: 8MHz or slower host processors, like the Teensy @ 3.3v or Ardunio
    // Pro Mini running at 3.3v, cannot handle this baud rate reliably due to
    // the baud timing being too misaligned with processor ticks. You must use
    // 38400 or slower in these cases, or use some kind of external separate
    // crystal solution for the UART timer.

// initialize device
    Serial.println(F("Initializing I2C devices..."));
    mpu.initialize();

// verify connection
    Serial.println(F("Testing device connections..."));
    Serial.println(mpu.testConnection() ? F("MPU6050 connection successful") : F("MPU6050 connection failed"));

// wait for ready
    Serial.println(F("\nSend any character to begin DMP programming and demo: "));
    while (Serial.available() && Serial.read()); // empty buffer
    while (Serial.available());                // wait for data
    while (Serial.available() && Serial.read()); // empty buffer again

// load and configure the DMP
    Serial.println(F("Initializing DMP..."));
    devStatus = mpu.dmpInitialize();

// supply your own gyro offsets here, scaled for min sensitivity
    mpu.setXGyroOffset(-61);
    mpu.setYGyroOffset(-10);
    mpu.setZGyroOffset(-80);
    mpu.setZAccelOffset(1012); // 1688 factory default for my test chip

// make sure it worked (returns 0 if so)
    if (devStatus == 0) {
        // turn on the DMP, now that it's ready
        Serial.println(F("Enabling DMP..."));
        mpu.setDMPEnabled(true);

// enable Arduino interrupt detection
        Serial.println(F("Enabling interrupt detection (Arduino external interrupt 0)..."));
        attachInterrupt(0, dmpDataReady, RISING);
        mpuIntStatus = mpu.getIntStatus();

// set our DMP Ready flag so the main loop() function knows it's okay to use it
        Serial.println(F("DMP ready! Waiting for first interrupt..."));
        dmpReady = true;

// get expected DMP packet size for later comparison
        packetSize = mpu.dmpGetFIFOPacketSize();
    } else {
        // ERROR!
        // 1 = initial memory load failed
        // 2 = DMP configuration updates failed
        // (if it's going to break, usually the code will be 1)
        Serial.print(F("DMP Initialization failed (code "));
        Serial.print(devStatus);
        Serial.println(F(")"));
    }

// configure LED for output
    pinMode(LED_PIN, OUTPUT);
    leftController.SetMode(AUTOMATIC);
}
void loop() {
    if (!dmpReady) return;
    while (!mpuInterrupt && fifoCount < packetSize) {
    }
    mpuInterrupt = false;
    mpuIntStatus = mpu.getIntStatus();
    fifoCount = mpu.getFIFOCount();
    if ((mpuIntStatus & 0x10) || fifoCount == 1024) {
        mpu.resetFIFO();
        Serial.println(F("FIFO overflow!"));
    } else if (mpuIntStatus & 0x02) {
        while (fifoCount < packetSize) fifoCount = mpu.getFIFOCount();
        mpu.getFIFOBytes(fifoBuffer, packetSize);
        fifoCount -= packetSize;
        blinkState = !blinkState;
        digitalWrite(LED_PIN, blinkState);
    }
            mpu.dmpGetQuaternion(&q, fifoBuffer);
            mpu.dmpGetGravity(&gravity, &q);
            mpu.dmpGetYawPitchRoll(ypr, &q, &gravity);
            Input=ypr[1];
            leftController.Compute();
            Serial.println(leftCorrection);
}